<?xml version="1.0" encoding="us-ascii" standalone="yes"?>
<!-- DFIN ActiveDisclosure(SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-02-27T17:11:18.9709146+00:00 -->
<!-- Version            : 5.0.1.321 -->
<!-- Package ID         : b6652a6e5569493b992345213d961e9a -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedNetLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedNetLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedPeriodEndLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedPeriodEndLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedPeriodStartLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedPeriodStartLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedTerseLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/negatedTotalLabel" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedTotalLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://www.xbrl.org/2009/role/netLabel" xlink:href="http://www.xbrl.org/lrr/role/net-2009-12-16.xsd#netLabel" xlink:type="simple" />
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/label/axisDefault" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-roles-2019-01-31.xsd#axisDefault" xlink:type="simple" />
  <link:labelLink xlink:role="http://www.xbrl.org/2003/role/link" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCentralIndexKey" xlink:type="locator" xlink:label="dei_EntityCentralIndexKey" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Central Index Key</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCentralIndexKey" xlink:to="dei_EntityCentralIndexKey_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LesseeOperatingLeaseLiabilityPaymentsDueYearFiveAndThereafter" xlink:type="locator" xlink:label="ctmx_LesseeOperatingLeaseLiabilityPaymentsDueYearFiveAndThereafter" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LesseeOperatingLeaseLiabilityPaymentsDueYearFiveAndThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lessee operating lease liability payments due year five and thereafter.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LesseeOperatingLeaseLiabilityPaymentsDueYearFiveAndThereafter" xlink:to="ctmx_LesseeOperatingLeaseLiabilityPaymentsDueYearFiveAndThereafter_lbl" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CoverAbstract" xlink:type="locator" xlink:label="dei_CoverAbstract" />
    <link:label xml:lang="en-US" xlink:label="dei_CoverAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cover [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CoverAbstract" xlink:to="dei_CoverAbstract_lbl" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentType" xlink:type="locator" xlink:label="dei_DocumentType" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentType_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentType" xlink:to="dei_DocumentType_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentType_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Type</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_AmendmentFlag" xlink:type="locator" xlink:label="dei_AmendmentFlag" />
    <link:label xml:lang="en-US" xlink:label="dei_AmendmentFlag_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amendment Flag</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_AmendmentFlag" xlink:to="dei_AmendmentFlag_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_AmendmentFlag_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amendment Flag</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentPeriodEndDate" xlink:type="locator" xlink:label="dei_DocumentPeriodEndDate" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Period End Date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentPeriodEndDate" xlink:to="dei_DocumentPeriodEndDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Period End Date</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:type="locator" xlink:label="dei_DocumentFiscalYearFocus" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Year Focus</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalYearFocus" xlink:to="dei_DocumentFiscalYearFocus_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Year Focus</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:type="locator" xlink:label="dei_DocumentFiscalPeriodFocus" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Period Focus</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalPeriodFocus" xlink:to="dei_DocumentFiscalPeriodFocus_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Period Focus</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_TradingSymbol" xlink:type="locator" xlink:label="dei_TradingSymbol" />
    <link:label xml:lang="en-US" xlink:label="dei_TradingSymbol_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Trading Symbol</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_TradingSymbol" xlink:to="dei_TradingSymbol_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_TradingSymbol_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Trading Symbol</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityRegistrantName" xlink:type="locator" xlink:label="dei_EntityRegistrantName" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityRegistrantName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Registrant Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityRegistrantName" xlink:to="dei_EntityRegistrantName_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityRegistrantName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Registrant Name</link:label>
    <link:label xml:lang="en-US" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Central Index Key</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:type="locator" xlink:label="dei_CurrentFiscalYearEndDate" />
    <link:label xml:lang="en-US" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Fiscal Year End Date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CurrentFiscalYearEndDate" xlink:to="dei_CurrentFiscalYearEndDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Current Fiscal Year End Date</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityWellKnownSeasonedIssuer" xlink:type="locator" xlink:label="dei_EntityWellKnownSeasonedIssuer" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Well-known Seasoned Issuer</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityWellKnownSeasonedIssuer" xlink:to="dei_EntityWellKnownSeasonedIssuer_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Well Known Seasoned Issuer</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityVoluntaryFilers" xlink:type="locator" xlink:label="dei_EntityVoluntaryFilers" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityVoluntaryFilers_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Voluntary Filers</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityVoluntaryFilers" xlink:to="dei_EntityVoluntaryFilers_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityVoluntaryFilers_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Voluntary Filers</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCurrentReportingStatus" xlink:type="locator" xlink:label="dei_EntityCurrentReportingStatus" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Current Reporting Status</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCurrentReportingStatus" xlink:to="dei_EntityCurrentReportingStatus_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Current Reporting Status</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFilerCategory" xlink:type="locator" xlink:label="dei_EntityFilerCategory" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFilerCategory_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Filer Category</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFilerCategory" xlink:to="dei_EntityFilerCategory_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFilerCategory_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Filer Category</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntitySmallBusiness" xlink:type="locator" xlink:label="dei_EntitySmallBusiness" />
    <link:label xml:lang="en-US" xlink:label="dei_EntitySmallBusiness_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Small Business</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntitySmallBusiness" xlink:to="dei_EntitySmallBusiness_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntitySmallBusiness_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Small Business</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityEmergingGrowthCompany" xlink:type="locator" xlink:label="dei_EntityEmergingGrowthCompany" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityEmergingGrowthCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Emerging Growth Company</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityEmergingGrowthCompany" xlink:to="dei_EntityEmergingGrowthCompany_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityEmergingGrowthCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Emerging Growth Company</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityShellCompany" xlink:type="locator" xlink:label="dei_EntityShellCompany" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityShellCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Shell Company</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityShellCompany" xlink:to="dei_EntityShellCompany_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityShellCompany_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Shell Company</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFileNumber" xlink:type="locator" xlink:label="dei_EntityFileNumber" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFileNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity File Number</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFileNumber" xlink:to="dei_EntityFileNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityFileNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity File Number</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityTaxIdentificationNumber" xlink:type="locator" xlink:label="dei_EntityTaxIdentificationNumber" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityTaxIdentificationNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Tax Identification Number</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityTaxIdentificationNumber" xlink:to="dei_EntityTaxIdentificationNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityTaxIdentificationNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Tax Identification Number</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressAddressLine1" xlink:type="locator" xlink:label="dei_EntityAddressAddressLine1" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line One</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressAddressLine1" xlink:to="dei_EntityAddressAddressLine1_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address Address Line1</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressAddressLine2" xlink:type="locator" xlink:label="dei_EntityAddressAddressLine2" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine2_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line Two</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressAddressLine2" xlink:to="dei_EntityAddressAddressLine2_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressAddressLine2_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address Address Line2</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressCityOrTown" xlink:type="locator" xlink:label="dei_EntityAddressCityOrTown" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, City or Town</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressCityOrTown" xlink:to="dei_EntityAddressCityOrTown_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address City Or Town</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressStateOrProvince" xlink:type="locator" xlink:label="dei_EntityAddressStateOrProvince" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, State or Province</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressStateOrProvince" xlink:to="dei_EntityAddressStateOrProvince_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address State Or Province</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressPostalZipCode" xlink:type="locator" xlink:label="dei_EntityAddressPostalZipCode" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Postal Zip Code</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityAddressPostalZipCode" xlink:to="dei_EntityAddressPostalZipCode_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address Postal Zip Code</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CityAreaCode" xlink:type="locator" xlink:label="dei_CityAreaCode" />
    <link:label xml:lang="en-US" xlink:label="dei_CityAreaCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">City Area Code</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CityAreaCode" xlink:to="dei_CityAreaCode_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_CityAreaCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">City Area Code</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LocalPhoneNumber" xlink:type="locator" xlink:label="dei_LocalPhoneNumber" />
    <link:label xml:lang="en-US" xlink:label="dei_LocalPhoneNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Local Phone Number</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_LocalPhoneNumber" xlink:to="dei_LocalPhoneNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_LocalPhoneNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Local Phone Number</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityInteractiveDataCurrent" xlink:type="locator" xlink:label="dei_EntityInteractiveDataCurrent" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Interactive Data Current</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityInteractiveDataCurrent" xlink:to="dei_EntityInteractiveDataCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Interactive Data Current</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_Security12bTitle" xlink:type="locator" xlink:label="dei_Security12bTitle" />
    <link:label xml:lang="en-US" xlink:label="dei_Security12bTitle_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of 12(b) Security</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_Security12bTitle" xlink:to="dei_Security12bTitle_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_Security12bTitle_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Security12b Title</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_SecurityExchangeName" xlink:type="locator" xlink:label="dei_SecurityExchangeName" />
    <link:label xml:lang="en-US" xlink:label="dei_SecurityExchangeName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Security Exchange Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_SecurityExchangeName" xlink:to="dei_SecurityExchangeName_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_SecurityExchangeName_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Security Exchange Name</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityIncorporationStateCountryCode" xlink:type="locator" xlink:label="dei_EntityIncorporationStateCountryCode" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Entity Incorporation, State or Country Code</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityIncorporationStateCountryCode" xlink:to="dei_EntityIncorporationStateCountryCode_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Incorporation State Country Code</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentAnnualReport" xlink:type="locator" xlink:label="dei_DocumentAnnualReport" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentAnnualReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Annual Report</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentAnnualReport" xlink:to="dei_DocumentAnnualReport_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentAnnualReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Annual Report</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentTransitionReport" xlink:type="locator" xlink:label="dei_DocumentTransitionReport" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentTransitionReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Transition Report</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentTransitionReport" xlink:to="dei_DocumentTransitionReport_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentTransitionReport_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Document Transition Report</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityPublicFloat" xlink:type="locator" xlink:label="dei_EntityPublicFloat" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityPublicFloat_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Public Float</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityPublicFloat" xlink:to="dei_EntityPublicFloat_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityPublicFloat_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Public Float</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:type="locator" xlink:label="dei_EntityCommonStockSharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Common Stock, Shares Outstanding</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCommonStockSharesOutstanding" xlink:to="dei_EntityCommonStockSharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Entity Common Stock Shares Outstanding</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementOfFinancialPositionAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfFinancialPositionAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Financial Position [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfFinancialPositionAbstract" xlink:to="us-gaap_StatementOfFinancialPositionAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:type="locator" xlink:label="us-gaap_StatementClassOfStockAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_StatementClassOfStockAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Class Of Stock [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:type="locator" xlink:label="us-gaap_ClassOfStockDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_ClassOfStockDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Stock [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:type="locator" xlink:label="us-gaap_ConvertiblePreferredStockMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertiblePreferredStockMember" xlink:to="us-gaap_ConvertiblePreferredStockMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConvertiblePreferredStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Convertible Preferred Stock [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsAbstract" xlink:type="locator" xlink:label="us-gaap_AssetsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:type="locator" xlink:label="us-gaap_AssetsCurrentAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current assets:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrentAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets Current [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and cash equivalents</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash And Cash Equivalents At Carrying Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term investments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities Debt Securities Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:type="locator" xlink:label="us-gaap_AccountsReceivableNetCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts receivable</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsReceivableNetCurrent" xlink:to="us-gaap_AccountsReceivableNetCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Receivable Net Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:type="locator" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prepaid expenses and other current assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Prepaid Expense And Other Assets Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsCurrent" xlink:type="locator" xlink:label="us-gaap_AssetsCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and equipment, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_PropertyPlantAndEquipmentNet_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Net</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:type="locator" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible assets, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Indefinite Lived Intangible Assets Excluding Goodwill</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Goodwill" xlink:type="locator" xlink:label="us-gaap_Goodwill" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Goodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Goodwill" xlink:to="us-gaap_Goodwill_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Goodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RestrictedCashNoncurrent" xlink:type="locator" xlink:label="us-gaap_RestrictedCashNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RestrictedCashNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted cash</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestrictedCashNoncurrent" xlink:to="us-gaap_RestrictedCashNoncurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RestrictedCashNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Cash Noncurrent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease right-of-use asset</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseRightOfUseAsset" xlink:to="us-gaap_OperatingLeaseRightOfUseAsset_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Right Of Use Asset</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:type="locator" xlink:label="us-gaap_OtherAssetsNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsNoncurrent" xlink:to="us-gaap_OtherAssetsNoncurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets Noncurrent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Assets" xlink:type="locator" xlink:label="us-gaap_Assets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Assets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Assets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liabilities and Stockholders&apos; Equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities And Stockholders Equity [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:type="locator" xlink:label="us-gaap_LiabilitiesCurrentAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current liabilities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities Current [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:type="locator" xlink:label="us-gaap_AccountsPayableCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableCurrent" xlink:to="us-gaap_AccountsPayableCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_AccruedLiabilitiesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Liabilities Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TaxesPayableCurrent" xlink:type="locator" xlink:label="us-gaap_TaxesPayableCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxesPayableCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income tax payable</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxesPayableCurrent" xlink:to="us-gaap_TaxesPayableCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxesPayableCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Taxes Payable Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred revenues, current portion</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiabilityCurrent" xlink:to="us-gaap_ContractWithCustomerLiabilityCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_LiabilitiesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiabilityNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred revenue, net of current portion</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiabilityNoncurrent" xlink:to="us-gaap_ContractWithCustomerLiabilityNoncurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Noncurrent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiabilityNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease liabilities - long term</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:to="us-gaap_OperatingLeaseLiabilityNoncurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liability Noncurrent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:type="locator" xlink:label="us-gaap_OtherLiabilitiesNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other long-term liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherLiabilitiesNoncurrent" xlink:to="us-gaap_OtherLiabilitiesNoncurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities Noncurrent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Liabilities" xlink:type="locator" xlink:label="us-gaap_Liabilities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Liabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Liabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:type="locator" xlink:label="us-gaap_CommitmentsAndContingencies" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and contingencies (Note 11)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingencies" xlink:to="us-gaap_CommitmentsAndContingencies_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_StockholdersEquityAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders&apos; equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockValue" xlink:type="locator" xlink:label="us-gaap_PreferredStockValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible preferred stock, $0.00001 par value; 10,000,000 shares authorized at December 31, 2019 and 2018; no shares issued and outstanding at December 31, 2019 and 2018, respectively</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockValue" xlink:to="us-gaap_PreferredStockValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockValue" xlink:type="locator" xlink:label="us-gaap_CommonStockValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, $0.00001 par value; 75,000,000 shares authorized at December 31, 2019 and 2018; 45,523,088 and 45,083,209 shares issued and outstanding at December 31, 2019 and 2018, respectively</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockValue" xlink:to="us-gaap_CommonStockValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:type="locator" xlink:label="us-gaap_AdditionalPaidInCapital" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional paid-in capital</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapital" xlink:to="us-gaap_AdditionalPaidInCapital_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid In Capital</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:type="locator" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated other comprehensive income (loss)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income Loss Net Of Tax</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated deficit</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings Accumulated Deficit</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquity" xlink:type="locator" xlink:label="us-gaap_StockholdersEquity" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total stockholders&apos; equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:type="locator" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities and stockholders&apos; equity</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities And Stockholders Equity</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:type="locator" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred stock, par value</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockParOrStatedValuePerShare" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Par Or Stated Value Per Share</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:type="locator" xlink:label="us-gaap_PreferredStockSharesAuthorized" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred stock, shares authorized</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesAuthorized" xlink:to="us-gaap_PreferredStockSharesAuthorized_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Shares Authorized</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:type="locator" xlink:label="us-gaap_PreferredStockSharesIssued" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred stock, shares issued</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Shares Issued</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_PreferredStockSharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred stock, shares outstanding</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesOutstanding" xlink:to="us-gaap_PreferredStockSharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Shares Outstanding</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:type="locator" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, par value</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Par Or Stated Value Per Share</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:type="locator" xlink:label="us-gaap_CommonStockSharesAuthorized" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares authorized</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesAuthorized" xlink:to="us-gaap_CommonStockSharesAuthorized_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Authorized</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:type="locator" xlink:label="us-gaap_CommonStockSharesIssued" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares issued</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesIssued" xlink:to="us-gaap_CommonStockSharesIssued_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Issued</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_CommonStockSharesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares outstanding</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesOutstanding" xlink:to="us-gaap_CommonStockSharesOutstanding_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Outstanding</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Income And Comprehensive Income [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" xlink:to="us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Revenues</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue From Contract With Customer Excluding Assessed Tax</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfRevenueExtensibleList" xlink:type="locator" xlink:label="us-gaap_TypeOfRevenueExtensibleList" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfRevenueExtensibleList_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Type of Revenue [Extensible List]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfRevenueExtensibleList" xlink:to="us-gaap_TypeOfRevenueExtensibleList_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfRevenueExtensibleList_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Type Of Revenue Extensible List</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingExpensesAbstract" xlink:type="locator" xlink:label="us-gaap_OperatingExpensesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpensesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating expenses:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingExpensesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpensesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Expenses [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Expense</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:type="locator" xlink:label="us-gaap_GeneralAndAdministrativeExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">General and administrative</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GeneralAndAdministrativeExpense" xlink:to="us-gaap_GeneralAndAdministrativeExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">General And Administrative Expense</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingExpenses" xlink:type="locator" xlink:label="us-gaap_OperatingExpenses" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpenses_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total operating expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingExpenses_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Expenses</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:type="locator" xlink:label="us-gaap_OperatingIncomeLoss" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Loss from operations</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Income Loss</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InvestmentIncomeInterest" xlink:type="locator" xlink:label="us-gaap_InvestmentIncomeInterest" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InvestmentIncomeInterest" xlink:to="us-gaap_InvestmentIncomeInterest_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Investment Income Interest</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:type="locator" xlink:label="us-gaap_OtherNonoperatingIncomeExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other expense, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherNonoperatingIncomeExpense" xlink:to="us-gaap_OtherNonoperatingIncomeExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Nonoperating Income Expense</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:type="locator" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Loss before income taxes</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_IncomeTaxExpenseBenefit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for (benefit from) income taxes</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxExpenseBenefit" xlink:to="us-gaap_IncomeTaxExpenseBenefit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Expense Benefit</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss" xlink:type="locator" xlink:label="us-gaap_NetIncomeLoss" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net loss</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Income Loss</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare" xlink:type="locator" xlink:label="us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss per share, basic and diluted</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare" xlink:to="us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Loss From Continuing Operations Per Basic And Diluted Share</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares used to compute net loss per share, basic and diluted</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted" xlink:to="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number Of Share Outstanding Basic And Diluted</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTaxAbstract" xlink:type="locator" xlink:label="us-gaap_OtherComprehensiveIncomeLossTaxAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherComprehensiveIncomeLossTaxAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss):</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherComprehensiveIncomeLossTaxAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossTaxAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherComprehensiveIncomeLossTaxAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income Loss Tax [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax" xlink:type="locator" xlink:label="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in unrealized gain (loss) on short-term investments, net of tax</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax" xlink:to="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect" xlink:type="locator" xlink:label="us-gaap_TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impact of adoption of new accounting pronouncement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect" xlink:to="us-gaap_TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tax Cuts And Jobs Act Of2017 Reclassification From Aoci To Retained Earnings Tax Effect</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:type="locator" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total comprehensive loss</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomeNetOfTax" xlink:to="us-gaap_ComprehensiveIncomeNetOfTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income Net Of Tax</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_StockIssuedDuringPeriodSharesStockPurchaseAgreement" xlink:type="locator" xlink:label="ctmx_StockIssuedDuringPeriodSharesStockPurchaseAgreement" />
    <link:label xml:lang="en-US" xlink:label="ctmx_StockIssuedDuringPeriodSharesStockPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of shares issued during the period as a result of an stock purchase agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_StockIssuedDuringPeriodSharesStockPurchaseAgreement" xlink:to="ctmx_StockIssuedDuringPeriodSharesStockPurchaseAgreement_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_StockIssuedDuringPeriodValueStockPurchaseAgreement" xlink:type="locator" xlink:label="ctmx_StockIssuedDuringPeriodValueStockPurchaseAgreement" />
    <link:label xml:lang="en-US" xlink:label="ctmx_StockIssuedDuringPeriodValueStockPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Aggregate change in value for stock issued during the period as a result of stock purchase agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_StockIssuedDuringPeriodValueStockPurchaseAgreement" xlink:to="ctmx_StockIssuedDuringPeriodValueStockPurchaseAgreement_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementOfStockholdersEquityAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Stockholders Equity [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfStockholdersEquityAbstract" xlink:to="us-gaap_StatementOfStockholdersEquityAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:type="locator" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Components</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_StatementEquityComponentsAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Equity Components [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Component</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_EquityComponentDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Equity Component [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockMember" xlink:type="locator" xlink:label="us-gaap_CommonStockMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockMember" xlink:to="us-gaap_CommonStockMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:type="locator" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-in Capital</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapitalMember" xlink:to="us-gaap_AdditionalPaidInCapitalMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid In Capital [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="locator" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Income/(Loss)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Deficit</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsMember" xlink:to="us-gaap_RetainedEarningsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:type="locator" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments for New Accounting Pronouncements</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments For New Accounting Pronouncements [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:type="locator" xlink:label="us-gaap_TypeOfAdoptionMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfAdoptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Type of Adoption</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="us-gaap_TypeOfAdoptionMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfAdoptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Type Of Adoption [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingStandardsUpdate201409Member" xlink:type="locator" xlink:label="us-gaap_AccountingStandardsUpdate201409Member" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingStandardsUpdate201409Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">ASU 2014-09</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountingStandardsUpdate201409Member" xlink:to="us-gaap_AccountingStandardsUpdate201409Member_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingStandardsUpdate201409Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update201409 [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingStandardsUpdate201802Member" xlink:type="locator" xlink:label="us-gaap_AccountingStandardsUpdate201802Member" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingStandardsUpdate201802Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ASU 2018-02</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountingStandardsUpdate201802Member" xlink:to="us-gaap_AccountingStandardsUpdate201802Member_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingStandardsUpdate201802Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update201802 [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning balance</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharesIssued" xlink:type="locator" xlink:label="us-gaap_SharesIssued" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning balance, shares</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesIssued" xlink:to="us-gaap_SharesIssued_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Issued</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1" xlink:type="locator" xlink:label="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impact of adoption of new accounting pronouncements</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1" xlink:to="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect On Retained Earnings Net Of Tax1</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock in follow-on offering, net of issuance costs</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value New Issues</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock in follow-on offering, net of issuance costs, shares</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares New Issues</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise of stock options</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:to="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value Stock Options Exercised</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise of stock options, shares</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Stock Options Exercised</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock under the Employee Stock Purchase Plan</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:to="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value Employee Stock Purchase Plan</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock under the Employee Stock Purchase Plan, shares</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:to="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Employee Stock Purchase Plans</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock to UCSB</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:to="us-gaap_StockIssuedDuringPeriodValueIssuedForServices_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value Issued For Services</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock to UCSB, shares</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:to="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Issued For Services</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_StockIssuedDuringPeriodValueStockPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock pursuant to the Amgen Stock Purchase Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_StockIssuedDuringPeriodValueStockPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Value Stock Purchase Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_StockIssuedDuringPeriodSharesStockPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock pursuant to the Amgen Stock Purchase Agreement, shares</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_StockIssuedDuringPeriodSharesStockPurchaseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Stock Purchase Agreement</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Other comprehensive income (loss)</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending balance</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending balance, shares</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_DepreciationAndAmortizationExcludingAmortizationOfIntangibleAssets" xlink:type="locator" xlink:label="ctmx_DepreciationAndAmortizationExcludingAmortizationOfIntangibleAssets" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DepreciationAndAmortizationExcludingAmortizationOfIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Depreciation and amortization excluding amortization of intangible assets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_DepreciationAndAmortizationExcludingAmortizationOfIntangibleAssets" xlink:to="ctmx_DepreciationAndAmortizationExcludingAmortizationOfIntangibleAssets_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_IncreaseDecreaseInAccruedLiabilitiesIncomeTaxPayableAndOtherLiabilitiesNoncurrent" xlink:type="locator" xlink:label="ctmx_IncreaseDecreaseInAccruedLiabilitiesIncomeTaxPayableAndOtherLiabilitiesNoncurrent" />
    <link:label xml:lang="en-US" xlink:label="ctmx_IncreaseDecreaseInAccruedLiabilitiesIncomeTaxPayableAndOtherLiabilitiesNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Increase (decrease) in accrued liabilities, income tax payable and other liabilities noncurrent.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_IncreaseDecreaseInAccruedLiabilitiesIncomeTaxPayableAndOtherLiabilitiesNoncurrent" xlink:to="ctmx_IncreaseDecreaseInAccruedLiabilitiesIncomeTaxPayableAndOtherLiabilitiesNoncurrent_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:type="locator" xlink:label="us-gaap_StatementOfCashFlowsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Of Cash Flows [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfCashFlowsAbstract" xlink:to="us-gaap_StatementOfCashFlowsAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from operating activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Operating Activities [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProfitLoss" xlink:type="locator" xlink:label="us-gaap_ProfitLoss" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProfitLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProfitLoss" xlink:to="us-gaap_ProfitLoss_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProfitLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Profit Loss</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments to reconcile net loss to net cash (used in) provided by operating activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:type="locator" xlink:label="us-gaap_AmortizationOfIntangibleAssets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of intangible assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfIntangibleAssets" xlink:to="us-gaap_AmortizationOfIntangibleAssets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amortization Of Intangible Assets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DepreciationAndAmortizationExcludingAmortizationOfIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DepreciationAndAmortizationExcludingAmortizationOfIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation And Amortization Excluding Amortization Of Intangible Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:type="locator" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Amortization of premium (accretion of discount) on investments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:to="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accretion Amortization Of Discounts And Premiums Investments</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensation" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:type="locator" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock in connection with UCSB sublicense fee</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:to="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Issuance Of Stock And Warrants For Services Or Claims</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentInProcess" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentInProcess" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentInProcess_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash acquisition of in process research and development asset charged to expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentInProcess" xlink:to="us-gaap_ResearchAndDevelopmentInProcess_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentInProcess_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development In Process</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredIncomeTaxesAndTaxCredits" xlink:type="locator" xlink:label="us-gaap_DeferredIncomeTaxesAndTaxCredits" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxesAndTaxCredits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred income taxes</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredIncomeTaxesAndTaxCredits" xlink:to="us-gaap_DeferredIncomeTaxesAndTaxCredits_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxesAndTaxCredits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income Taxes And Tax Credits</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in operating assets and liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Operating Capital [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accounts receivable</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accounts Receivable</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivableRelatedParties" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivableRelatedParties" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivableRelatedParties_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Related party accounts receivable</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsReceivableRelatedParties" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivableRelatedParties_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivableRelatedParties_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accounts Receivable Related Parties</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Prepaid expenses and other current assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Prepaid Deferred Expense And Other Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:to="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Other Operating Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsPayable" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accounts Payable</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_IncreaseDecreaseInAccruedLiabilitiesIncomeTaxPayableAndOtherLiabilitiesNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued liabilities, income tax payable and other long-term liabilities</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_IncreaseDecreaseInAccruedLiabilitiesIncomeTaxPayableAndOtherLiabilitiesNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Accrued Liabilities Income Tax Payable And Other Liabilities Noncurrent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInContractWithCustomerLiability" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred revenue</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInContractWithCustomerLiability" xlink:to="us-gaap_IncreaseDecreaseInContractWithCustomerLiability_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncreaseDecreaseInContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Contract With Customer Liability</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash (used in) provided by operating activities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Operating Activities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from investing activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Investing Activities [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of property and equipment</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments To Acquire Property Plant And Equipment</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of short-term investments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt" xlink:to="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments To Acquire Available For Sale Securities Debt</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt" xlink:type="locator" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maturities of short-term investments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt" xlink:to="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Sale Of Available For Sale Securities Debt</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by (used in) investing activities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Investing Activities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from financing activities:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Financing Activities [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:type="locator" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from issuance of common stock, net of issuance costs</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Common Stock</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" xlink:type="locator" xlink:label="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from employee stock purchase plan and exercise of stock options</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" xlink:to="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by financing activities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided By Used In Financing Activities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" xlink:type="locator" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net (decrease) increase in cash, cash equivalents and restricted cash</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:type="locator" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash, cash equivalents and restricted cash, beginning of year</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash, cash equivalents and restricted cash, end of year</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="locator" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental disclosures of cash flow information:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Cash Flow Information [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxesPaid" xlink:type="locator" xlink:label="us-gaap_IncomeTaxesPaid" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxesPaid_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for income taxes</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxesPaid" xlink:to="us-gaap_IncomeTaxesPaid_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxesPaid_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Taxes Paid</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:type="locator" xlink:label="us-gaap_NoncashInvestingAndFinancingItemsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NoncashInvestingAndFinancingItemsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental disclosures of noncash investing items:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NoncashInvestingAndFinancingItemsAbstract" xlink:to="us-gaap_NoncashInvestingAndFinancingItemsAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NoncashInvestingAndFinancingItemsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Noncash Investing And Financing Items [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:type="locator" xlink:label="us-gaap_CapitalExpendituresIncurredButNotYetPaid" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CapitalExpendituresIncurredButNotYetPaid_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Purchases of property and equipment in accounts payable and accrued liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:to="us-gaap_CapitalExpendituresIncurredButNotYetPaid_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CapitalExpendituresIncurredButNotYetPaid_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Capital Expenditures Incurred But Not Yet Paid</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentsIncorporatedByReferenceTextBlock" xlink:type="locator" xlink:label="dei_DocumentsIncorporatedByReferenceTextBlock" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentsIncorporatedByReferenceTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Documents Incorporated by Reference</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentsIncorporatedByReferenceTextBlock" xlink:to="dei_DocumentsIncorporatedByReferenceTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="dei_DocumentsIncorporatedByReferenceTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Documents Incorporated By Reference [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureTextBlockAbstract" xlink:type="locator" xlink:label="us-gaap_DisclosureTextBlockAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisclosureTextBlockAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disclosure Text Block [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisclosureTextBlockAbstract" xlink:to="us-gaap_DisclosureTextBlockAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NatureOfOperations" xlink:type="locator" xlink:label="us-gaap_NatureOfOperations" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NatureOfOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Description of the Business</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NatureOfOperations" xlink:to="us-gaap_NatureOfOperations_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NatureOfOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Nature Of Operations</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingPoliciesAbstract" xlink:type="locator" xlink:label="us-gaap_AccountingPoliciesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingPoliciesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Policies [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountingPoliciesAbstract" xlink:to="us-gaap_AccountingPoliciesAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" xlink:type="locator" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation and Summary of Significant Accounting Policies</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock" xlink:to="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Basis Of Presentation And Significant Accounting Policies [Text Block]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AdoptedAndRecentAccountingPronouncementsTextBlock" xlink:type="locator" xlink:label="ctmx_AdoptedAndRecentAccountingPronouncementsTextBlock" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AdoptedAndRecentAccountingPronouncementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Adopted and recent accounting pronouncements.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AdoptedAndRecentAccountingPronouncementsTextBlock" xlink:to="ctmx_AdoptedAndRecentAccountingPronouncementsTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AdoptedAndRecentAccountingPronouncementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adopted and Recent Accounting Pronouncements</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AdoptedAndRecentAccountingPronouncementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Adopted And Recent Accounting Pronouncements [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareTextBlock" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net Loss Per Share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareTextBlock" xlink:to="us-gaap_EarningsPerShareTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueDisclosuresAbstract" xlink:type="locator" xlink:label="us-gaap_FairValueDisclosuresAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueDisclosuresAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueDisclosuresAbstract" xlink:to="us-gaap_FairValueDisclosuresAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:type="locator" xlink:label="us-gaap_FairValueDisclosuresTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurements and Short-Term Investments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueDisclosuresTextBlock" xlink:to="us-gaap_FairValueDisclosuresTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAbstract" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and Equipment</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Disclosure [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill And Intangible Assets Disclosure [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:to="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill and Intangible Assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:to="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill And Intangible Assets Disclosure [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:type="locator" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Liabilities Current [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued Liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable And Accrued Liabilities Disclosure [Text Block]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ResearchAndCollaborationAgreementsTextBlock" xlink:type="locator" xlink:label="ctmx_ResearchAndCollaborationAgreementsTextBlock" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchAndCollaborationAgreementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Research and collaboration agreements.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ResearchAndCollaborationAgreementsTextBlock" xlink:to="ctmx_ResearchAndCollaborationAgreementsTextBlock_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:type="locator" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Organization Consolidation And Presentation Of Financial Statements [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:to="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchAndCollaborationAgreementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Collaboration Agreements</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchAndCollaborationAgreementsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Collaboration Agreements [Text Block]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LicenseAgreementDisclosureTextBlock" xlink:type="locator" xlink:label="ctmx_LicenseAgreementDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseAgreementDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LicenseAgreementDisclosureTextBlock" xlink:to="ctmx_LicenseAgreementDisclosureTextBlock_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentAbstract" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentAbstract" xlink:to="us-gaap_ResearchAndDevelopmentAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseAgreementDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseAgreementDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement Disclosure [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies Disclosure [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and Contingencies</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies Disclosure [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LeasesAbstract" xlink:type="locator" xlink:label="us-gaap_LeasesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeasesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Leases [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeasesAbstract" xlink:to="us-gaap_LeasesAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeasesTextBlock" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeasesTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeasesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Leases</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeasesTextBlock" xlink:to="us-gaap_LesseeOperatingLeasesTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeasesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Leases [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityAbstract" xlink:type="locator" xlink:label="us-gaap_EquityAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EquityAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Equity [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityAbstract" xlink:to="us-gaap_EquityAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:to="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders Equity Note Disclosure [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:type="locator" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:to="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:type="locator" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based Compensation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock" xlink:to="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disclosure Of Compensation Related Costs Share Based Payments [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_IncomeTaxDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Disclosure [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxDisclosureAbstract" xlink:to="us-gaap_IncomeTaxDisclosureAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Taxes</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxDisclosureTextBlock" xlink:to="us-gaap_IncomeTaxDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Disclosure [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CompensationAndRetirementDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_CompensationAndRetirementDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CompensationAndRetirementDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Compensation And Retirement Disclosure [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CompensationAndRetirementDisclosureAbstract" xlink:to="us-gaap_CompensationAndRetirementDisclosureAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:type="locator" xlink:label="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Defined Contribution Plan</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:to="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Pension And Other Postretirement Benefits Disclosure [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_QuarterlyFinancialInformationDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_QuarterlyFinancialInformationDisclosureAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_QuarterlyFinancialInformationDisclosureAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Quarterly Financial Information Disclosure [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_QuarterlyFinancialInformationDisclosureAbstract" xlink:to="us-gaap_QuarterlyFinancialInformationDisclosureAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_QuarterlyFinancialInformationTextBlock" xlink:type="locator" xlink:label="us-gaap_QuarterlyFinancialInformationTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_QuarterlyFinancialInformationTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplementary Data &#8211; Quarterly Financial Data (Unaudited)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_QuarterlyFinancialInformationTextBlock" xlink:to="us-gaap_QuarterlyFinancialInformationTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_QuarterlyFinancialInformationTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Quarterly Financial Information [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventsAbstract" xlink:type="locator" xlink:label="us-gaap_SubsequentEventsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Events [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventsAbstract" xlink:to="us-gaap_SubsequentEventsAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventsTextBlock" xlink:type="locator" xlink:label="us-gaap_SubsequentEventsTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Events</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventsTextBlock" xlink:to="us-gaap_SubsequentEventsTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Events [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Basis Of Accounting Policy Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_UseOfEstimates" xlink:type="locator" xlink:label="us-gaap_UseOfEstimates" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Use of Estimates</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UseOfEstimates" xlink:to="us-gaap_UseOfEstimates_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Use Of Estimates</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskCreditRisk" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskCreditRisk" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskCreditRisk_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration of Credit Risk and Other Risks and Uncertainties</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskCreditRisk" xlink:to="us-gaap_ConcentrationRiskCreditRisk_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskCreditRisk_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk Credit Risk</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentReportingPolicyPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SegmentReportingPolicyPolicyTextBlock" xlink:to="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting Policy Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and Cash Equivalents</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:to="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash And Cash Equivalents Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted Cash</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy" xlink:to="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash And Cash Equivalents Restricted Cash And Cash Equivalents Policy</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MarketableSecuritiesPolicy" xlink:type="locator" xlink:label="us-gaap_MarketableSecuritiesPolicy" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MarketableSecuritiesPolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term Investments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MarketableSecuritiesPolicy" xlink:to="us-gaap_MarketableSecuritiesPolicy_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MarketableSecuritiesPolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Marketable Securities Policy</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and Equipment, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill and Intangible Assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" xlink:to="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill And Intangible Assets Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impairment of Long-Lived Assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock" xlink:to="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ImpairmentOrDisposalOfLongLivedAssetsPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Impairment Or Disposal Of Long Lived Assets Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRecognitionPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue Recognition</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRecognitionPolicyTextBlock" xlink:to="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Recognition Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Comprehensive Loss</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" xlink:to="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income Policy Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueFromContractWithCustomerPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract Balances</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock" xlink:to="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue From Contract With Customer Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-Based Compensation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy" xlink:to="us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Option And Incentive Plans Policy</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_IncomeTaxPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Taxes</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxPolicyTextBlock" xlink:to="us-gaap_IncomeTaxPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:to="us-gaap_ResearchAndDevelopmentExpensePolicy_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Expense Policy</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeLeasesPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_LesseeLeasesPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeLeasesPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Leases</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeLeasesPolicyTextBlock" xlink:to="us-gaap_LesseeLeasesPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeLeasesPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Leases Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:type="locator" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adopted Accounting Pronouncements and Recent Accounting Pronouncements</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:to="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">New Accounting Pronouncements Policy Policy [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SchedulesOfConcentrationOfRiskByRiskFactorTextBlock" xlink:type="locator" xlink:label="us-gaap_SchedulesOfConcentrationOfRiskByRiskFactorTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SchedulesOfConcentrationOfRiskByRiskFactorTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Customers and Collaboration Partners who Represent 10% or More of Total Revenue During Each Period Presented or Net Accounts Receivable Balance</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SchedulesOfConcentrationOfRiskByRiskFactorTextBlock" xlink:to="us-gaap_SchedulesOfConcentrationOfRiskByRiskFactorTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SchedulesOfConcentrationOfRiskByRiskFactorTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedules Of Concentration Of Risk By Risk Factor [Text Block]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock" xlink:type="locator" xlink:label="ctmx_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of cash, cash equivalents, and restricted cash.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock" xlink:to="ctmx_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Cash, Cash Equivalents, and Restricted Cash</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Cash Cash Equivalents And Restricted Cash Table [Text Block]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock" xlink:type="locator" xlink:label="ctmx_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Tabular disclosure of property plant and equipment estimated useful lives.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock" xlink:to="ctmx_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Useful Lives of Property and Equipment</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Estimated Useful Lives Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Short-Term Investments Subject to Fair Value Measurements on a Recurring Basis</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:to="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Fair Value Assets And Liabilities Measured On Recurring Basis Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Property and Equipment, Net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfIntangibleAssetsAndGoodwillTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfIntangibleAssetsAndGoodwillTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfIntangibleAssetsAndGoodwillTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Goodwill and Intangible Assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfIntangibleAssetsAndGoodwillTableTextBlock" xlink:to="us-gaap_ScheduleOfIntangibleAssetsAndGoodwillTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfIntangibleAssetsAndGoodwillTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Intangible Assets And Goodwill Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Accrued Liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" xlink:to="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Accrued Liabilities Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisaggregationOfRevenueTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Revenue by Collaboration Partner</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:to="us-gaap_DisaggregationOfRevenueTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DisaggregationOfRevenueTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Disaggregation Of Revenue Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Contract Liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock" xlink:to="us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Asset And Liability Table [Text Block]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SupplementalInformationRelatedToLeasesTableTextBlock" xlink:type="locator" xlink:label="ctmx_SupplementalInformationRelatedToLeasesTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SupplementalInformationRelatedToLeasesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Supplemental information related to leases.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SupplementalInformationRelatedToLeasesTableTextBlock" xlink:to="ctmx_SupplementalInformationRelatedToLeasesTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SupplementalInformationRelatedToLeasesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Supplemental Information Related to Leases</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SupplementalInformationRelatedToLeasesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Information Related To Leases Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfStockByClassTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfStockByClassTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfStockByClassTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Reserved Shares of Common Stock Issuance on Converted Basis</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfStockByClassTextBlock" xlink:to="us-gaap_ScheduleOfStockByClassTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfStockByClassTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Stock By Class [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Activity Under Company&apos;s Stock Option Plans</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" xlink:to="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Share Based Compensation Stock Options Activity Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total Stock-based Compensation Recognized</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock" xlink:to="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Estimated Fair Value of Employee Stock Options and ESPP Using Black-Scholes Valuation Model</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" xlink:to="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Share Based Payment Award Stock Options Valuation Assumptions Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Components of Provision for (Benefit from) Income Taxes</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" xlink:to="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Components Of Income Tax Expense Benefit Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Effective Tax Rate Reconciliation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock" xlink:to="us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Effective Income Tax Rate Reconciliation Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Deferred Income Tax Liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" xlink:to="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Deferred Tax Assets And Liabilities Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SummaryOfIncomeTaxContingenciesTextBlock" xlink:type="locator" xlink:label="us-gaap_SummaryOfIncomeTaxContingenciesTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SummaryOfIncomeTaxContingenciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Reconciliation of Unrecognized Tax Benefits</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SummaryOfIncomeTaxContingenciesTextBlock" xlink:to="us-gaap_SummaryOfIncomeTaxContingenciesTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SummaryOfIncomeTaxContingenciesTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Summary Of Income Tax Contingencies [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfQuarterlyFinancialInformationTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ScheduleOfQuarterlyFinancialInformationTableTextBlock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfQuarterlyFinancialInformationTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unaudited Financial Information</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfQuarterlyFinancialInformationTableTextBlock" xlink:to="us-gaap_ScheduleOfQuarterlyFinancialInformationTableTextBlock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfQuarterlyFinancialInformationTableTextBlock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Quarterly Financial Information Table [Text Block]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskTable" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskTable" xlink:to="us-gaap_ConcentrationRiskTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MajorCustomersAxis" xlink:type="locator" xlink:label="srt_MajorCustomersAxis" />
    <link:label xml:lang="en-US" xlink:label="srt_MajorCustomersAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Customer</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_MajorCustomersAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_MajorCustomersAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Major Customers [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_NameOfMajorCustomerDomain" xlink:type="locator" xlink:label="srt_NameOfMajorCustomerDomain" />
    <link:label xml:lang="en-US" xlink:label="srt_NameOfMajorCustomerDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Customer</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_NameOfMajorCustomerDomain" xlink:to="srt_NameOfMajorCustomerDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_NameOfMajorCustomerDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Name Of Major Customer [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MajorCustomerMember" xlink:type="locator" xlink:label="ctmx_MajorCustomerMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MajorCustomerMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Major customer [Member].</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MajorCustomerMember" xlink:to="ctmx_MajorCustomerMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MajorCustomerMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Major Customer</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MajorCustomerMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Major Customer [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_CounterpartyNameAxis" xlink:type="locator" xlink:label="srt_CounterpartyNameAxis" />
    <link:label xml:lang="en-US" xlink:label="srt_CounterpartyNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Counterparty Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_CounterpartyNameAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_CounterpartyNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Counterparty Name [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:type="locator" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <link:label xml:lang="en-US" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Counterparty Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Repurchase Agreement Counterparty Name [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AbbVieIrelandUnlimitedCompanyMember" xlink:type="locator" xlink:label="ctmx_AbbVieIrelandUnlimitedCompanyMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AbbVieIrelandUnlimitedCompanyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">AbbVie Ireland Unlimited Company.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AbbVieIrelandUnlimitedCompanyMember" xlink:to="ctmx_AbbVieIrelandUnlimitedCompanyMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AbbVieIrelandUnlimitedCompanyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">AbbVie Ireland Unlimited Company</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AbbVieIrelandUnlimitedCompanyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Abb Vie Ireland Unlimited Company [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_BristolMyersSquibbCompanyMember" xlink:type="locator" xlink:label="ctmx_BristolMyersSquibbCompanyMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_BristolMyersSquibbCompanyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Bristol-Myers Squibb Company.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_BristolMyersSquibbCompanyMember" xlink:to="ctmx_BristolMyersSquibbCompanyMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_BristolMyersSquibbCompanyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Bristol Myers Squibb Company</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_BristolMyersSquibbCompanyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Bristol Myers Squibb Company [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ImmunoGenIncMember" xlink:type="locator" xlink:label="ctmx_ImmunoGenIncMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ImmunoGenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">ImmunoGen, Inc.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ImmunoGenIncMember" xlink:to="ctmx_ImmunoGenIncMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ImmunoGenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Immuno Gen Inc</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ImmunoGenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Immuno Gen Inc [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskLineItems" xlink:type="locator" xlink:label="us-gaap_ConcentrationRiskLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskLineItems" xlink:to="us-gaap_ConcentrationRiskLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConcentrationRiskLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveTerseLabel">Revenue</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveTerseLabel">Accounts Receivable, net</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfBusinessActivities" xlink:type="locator" xlink:label="ctmx_NumberOfBusinessActivities" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfBusinessActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of business activities.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfBusinessActivities" xlink:to="ctmx_NumberOfBusinessActivities_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SummaryOfSignificantAccountingPoliciesLineItems" xlink:type="locator" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesLineItems" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Summary of significant accounting policies.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="ctmx_SummaryOfSignificantAccountingPoliciesLineItems_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SummaryOfSignificantAccountingPoliciesTable" xlink:type="locator" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesTable" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Summary of significant accounting policies.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SummaryOfSignificantAccountingPoliciesTable" xlink:to="ctmx_SummaryOfSignificantAccountingPoliciesTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary Of Significant Accounting Policies [Table]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Summary Of Significant Accounting Policies [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis" xlink:type="locator" xlink:label="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Initial Application Period Cumulative Effect Transition</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis" xlink:to="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Initial Application Period Cumulative Effect Transition [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InitialApplicationPeriodCumulativeEffectTransitionDomain" xlink:type="locator" xlink:label="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Initial Application Period Cumulative Effect Transition</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionDomain" xlink:to="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InitialApplicationPeriodCumulativeEffectTransitionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Initial Application Period Cumulative Effect Transition [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member" xlink:type="locator" xlink:label="us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member" xlink:to="us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Difference Between Revenue Guidance In Effect Before And After Topic606 [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingStandardsUpdate201409Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ASC 606</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finite-Lived Intangible Assets by Major Class</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finite Lived Intangible Assets By Major Class [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finite-Lived Intangible Assets, Major Class Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finite Lived Intangible Assets Major Class Name [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ProbodyTechnologyMember" xlink:type="locator" xlink:label="ctmx_ProbodyTechnologyMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ProbodyTechnologyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Probody technology.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ProbodyTechnologyMember" xlink:to="ctmx_ProbodyTechnologyMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ProbodyTechnologyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Probody technology</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ProbodyTechnologyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Probody Technology [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary Of Significant Accounting Policies [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Summary Of Significant Accounting Policies [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfBusinessActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of business activities</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfBusinessActivities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Business Activities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NumberOfOperatingSegments" xlink:type="locator" xlink:label="us-gaap_NumberOfOperatingSegments" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NumberOfOperatingSegments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of operating segments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NumberOfOperatingSegments" xlink:to="us-gaap_NumberOfOperatingSegments_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_NumberOfOperatingSegments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Operating Segments</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsAbstract" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashAndCashEquivalentsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash And Cash Equivalents [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:type="locator" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Cash, cash equivalents, and restricted cash</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Property Plant And Equipment [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Property Plant And Equipment [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property, Plant and Equipment, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment By Type [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property, Plant and Equipment, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Type [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MachineryAndEquipmentMember" xlink:type="locator" xlink:label="us-gaap_MachineryAndEquipmentMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MachineryAndEquipmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Machinery and equipment</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MachineryAndEquipmentMember" xlink:to="us-gaap_MachineryAndEquipmentMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MachineryAndEquipmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Machinery And Equipment [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ComputerEquipmentAndSoftwareMember" xlink:type="locator" xlink:label="ctmx_ComputerEquipmentAndSoftwareMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ComputerEquipmentAndSoftwareMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Computer equipment and software.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ComputerEquipmentAndSoftwareMember" xlink:to="ctmx_ComputerEquipmentAndSoftwareMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ComputerEquipmentAndSoftwareMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Computer equipment and software</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ComputerEquipmentAndSoftwareMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Computer Equipment And Software [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:type="locator" xlink:label="us-gaap_FurnitureAndFixturesMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FurnitureAndFixturesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Furniture and fixtures</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FurnitureAndFixturesMember" xlink:to="us-gaap_FurnitureAndFixturesMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FurnitureAndFixturesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Furniture And Fixtures [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:type="locator" xlink:label="us-gaap_LeaseholdImprovementsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseholdImprovementsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Leasehold improvements</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseholdImprovementsMember" xlink:to="us-gaap_LeaseholdImprovementsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseholdImprovementsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Leasehold Improvements [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property Plant And Equipment [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated useful life of property and equipment</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:to="us-gaap_PropertyPlantAndEquipmentUsefulLife_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Useful Life</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentEstimatedUsefulLives" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentEstimatedUsefulLives" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentEstimatedUsefulLives_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated useful life of leasehold improvements, description</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentEstimatedUsefulLives" xlink:to="us-gaap_PropertyPlantAndEquipmentEstimatedUsefulLives_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentEstimatedUsefulLives_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Estimated Useful Lives</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillImpairmentLoss" xlink:type="locator" xlink:label="us-gaap_GoodwillImpairmentLoss" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GoodwillImpairmentLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impairment of goodwill</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillImpairmentLoss" xlink:to="us-gaap_GoodwillImpairmentLoss_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GoodwillImpairmentLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill Impairment Loss</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:type="locator" xlink:label="us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impairment of intangible assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:to="us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Impairment Of Intangible Assets Indefinitelived Excluding Goodwill</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse" xlink:type="locator" xlink:label="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impairment of long-lived assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse" xlink:to="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Impairment Of Long Lived Assets Held For Use</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Increase in accumulated deficit balance</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1" xlink:type="locator" xlink:label="us-gaap_FinitelivedIntangibleAssetsAcquired1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinitelivedIntangibleAssetsAcquired1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Acquired, technology know-how</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FinitelivedIntangibleAssetsAcquired1" xlink:to="us-gaap_FinitelivedIntangibleAssetsAcquired1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FinitelivedIntangibleAssetsAcquired1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finitelived Intangible Assets Acquired1</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Research and development expense</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingStandardsUpdate201602Member" xlink:type="locator" xlink:label="us-gaap_AccountingStandardsUpdate201602Member" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingStandardsUpdate201602Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ASC 842</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountingStandardsUpdate201602Member" xlink:to="us-gaap_AccountingStandardsUpdate201602Member_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccountingStandardsUpdate201602Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update201602 [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Right-of-use asset</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiability" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiability" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Lease liability</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiability" xlink:to="us-gaap_OperatingLeaseLiability_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liability</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Increase in other comprehensive income</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:type="locator" xlink:label="us-gaap_DerivativeInstrumentRiskAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instrument</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeInstrumentRiskAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instrument Risk [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:type="locator" xlink:label="us-gaap_DerivativeContractTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Contract</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_DerivativeContractTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Contract Type [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockOptionMember" xlink:type="locator" xlink:label="us-gaap_StockOptionMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options to purchase common stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockOptionMember" xlink:to="us-gaap_StockOptionMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Option [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Anti-dilutive securities excluded from computation of diluted net loss per share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Hierarchy and NAV</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value By Fair Value Hierarchy Level [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Hierarchy and NAV</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurements Fair Value Hierarchy [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level I</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsLevel1Member" xlink:to="us-gaap_FairValueInputsLevel1Member_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Inputs Level1 [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByAssetClassAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByAssetClassAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueByAssetClassAxis" xlink:to="us-gaap_FairValueByAssetClassAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value By Asset Class [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation By Asset Class [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MoneyMarketFundsMember" xlink:type="locator" xlink:label="us-gaap_MoneyMarketFundsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MoneyMarketFundsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Money market funds</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MoneyMarketFundsMember" xlink:to="us-gaap_MoneyMarketFundsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MoneyMarketFundsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Money Market Funds [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MoneyMarketFundsIncludedInRestrictedCashMember" xlink:type="locator" xlink:label="ctmx_MoneyMarketFundsIncludedInRestrictedCashMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MoneyMarketFundsIncludedInRestrictedCashMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Money market funds included in restricted cash.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MoneyMarketFundsIncludedInRestrictedCashMember" xlink:to="ctmx_MoneyMarketFundsIncludedInRestrictedCashMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MoneyMarketFundsIncludedInRestrictedCashMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted cash (money market funds)</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MoneyMarketFundsIncludedInRestrictedCashMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Money Market Funds Included In Restricted Cash [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:type="locator" xlink:label="us-gaap_USTreasuryAndGovernmentMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_USTreasuryAndGovernmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">U. S. Government bonds</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_USTreasuryAndGovernmentMember" xlink:to="us-gaap_USTreasuryAndGovernmentMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_USTreasuryAndGovernmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">U S Treasury And Government [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAmortizedCost" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesAmortizedCost" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesAmortizedCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Amortized Cost</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleSecuritiesAmortizedCost" xlink:to="us-gaap_AvailableForSaleSecuritiesAmortizedCost_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesAmortizedCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities Amortized Cost</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross Unrealized Holding Gains</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:to="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Gross Unrealized Holding Losses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:to="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecurities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate Fair Value</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleSecurities" xlink:to="us-gaap_AvailableForSaleSecurities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Amortized Cost</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Debt Securities Amortized Cost Basis</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross Unrealized Holding Gains</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Gross Unrealized Holding Losses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate Fair Value</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities Debt Securities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Contractual maturities of longer than one year</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Available For Sale Securities Debt Maturities Within One Year Fair Value</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ComputerEquipmentAndSoftwareGross" xlink:type="locator" xlink:label="ctmx_ComputerEquipmentAndSoftwareGross" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ComputerEquipmentAndSoftwareGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Computer equipment and software gross.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ComputerEquipmentAndSoftwareGross" xlink:to="ctmx_ComputerEquipmentAndSoftwareGross_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MachineryAndEquipmentGross" xlink:type="locator" xlink:label="us-gaap_MachineryAndEquipmentGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MachineryAndEquipmentGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Machinery and equipment</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MachineryAndEquipmentGross" xlink:to="us-gaap_MachineryAndEquipmentGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_MachineryAndEquipmentGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Machinery And Equipment Gross</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ComputerEquipmentAndSoftwareGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Computer equipment and software</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ComputerEquipmentAndSoftwareGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Computer Equipment And Software Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FurnitureAndFixturesGross" xlink:type="locator" xlink:label="us-gaap_FurnitureAndFixturesGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FurnitureAndFixturesGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Furniture and fixtures</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FurnitureAndFixturesGross" xlink:to="us-gaap_FurnitureAndFixturesGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FurnitureAndFixturesGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Furniture And Fixtures Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LeaseholdImprovementsGross" xlink:type="locator" xlink:label="us-gaap_LeaseholdImprovementsGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseholdImprovementsGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Leasehold improvements</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseholdImprovementsGross" xlink:to="us-gaap_LeaseholdImprovementsGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseholdImprovementsGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Leasehold Improvements Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConstructionInProgressGross" xlink:type="locator" xlink:label="us-gaap_ConstructionInProgressGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConstructionInProgressGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Construction in progress</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConstructionInProgressGross" xlink:to="us-gaap_ConstructionInProgressGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ConstructionInProgressGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Construction In Progress Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total property and equipment</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentGross" xlink:to="us-gaap_PropertyPlantAndEquipmentGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Property Plant And Equipment Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less: accumulated depreciation and amortization</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Depreciation Depletion And Amortization Property Plant And Equipment</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Property and equipment, net</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Depreciation" xlink:type="locator" xlink:label="us-gaap_Depreciation" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Depreciation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Depreciation" xlink:to="us-gaap_Depreciation_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Depreciation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Finite Lived Intangible Assets [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Finite Lived Intangible Assets [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember" xlink:type="locator" xlink:label="us-gaap_InProcessResearchAndDevelopmentMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InProcessResearchAndDevelopmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">IPR&amp;D [Member]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InProcessResearchAndDevelopmentMember" xlink:to="us-gaap_InProcessResearchAndDevelopmentMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_InProcessResearchAndDevelopmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">In Process Research And Development [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finite Lived Intangible Assets [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finite Lived Intangible Assets [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:type="locator" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Average estimated lives of patents</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:to="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Acquired Finite Lived Intangible Assets Weighted Average Useful Life</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Amortization expense of intangible assets</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_GoodwillAbstract" xlink:type="locator" xlink:label="ctmx_GoodwillAbstract" />
    <link:label xml:lang="en-US" xlink:label="ctmx_GoodwillAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Goodwill.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_GoodwillAbstract" xlink:to="ctmx_GoodwillAbstract_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_GoodwillAndIntangibleAssetsLineItems" xlink:type="locator" xlink:label="ctmx_GoodwillAndIntangibleAssetsLineItems" />
    <link:label xml:lang="en-US" xlink:label="ctmx_GoodwillAndIntangibleAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Goodwill and intangible assets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_GoodwillAndIntangibleAssetsLineItems" xlink:to="ctmx_GoodwillAndIntangibleAssetsLineItems_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable" xlink:type="locator" xlink:label="ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of goodwill and intangible assets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable" xlink:to="ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Goodwill And Intangible Assets [Table]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Goodwill And Intangible Assets [Table]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_InProcessResearchAndDevelopmentMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">In-Process Research and Development</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_GoodwillAndIntangibleAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill And Intangible Assets [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_GoodwillAndIntangibleAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill And Intangible Assets [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_GoodwillAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_GoodwillAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNetAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNetAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNetAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finite Lived Intangible Assets Net [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Intangible assets, gross</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsGross" xlink:to="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finite Lived Intangible Assets Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less accumulated amortization</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finite Lived Intangible Assets Accumulated Amortization</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Intangible assets, net</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNet" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Finite Lived Intangible Assets Net</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AccruedResearchAndClinicalCurrent" xlink:type="locator" xlink:label="ctmx_AccruedResearchAndClinicalCurrent" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AccruedResearchAndClinicalCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Accrued research and clinical current.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AccruedResearchAndClinicalCurrent" xlink:to="ctmx_AccruedResearchAndClinicalCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AccruedResearchAndClinicalCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and clinical expenses</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AccruedResearchAndClinicalCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Research And Clinical Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payroll and related expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeRelatedLiabilitiesCurrent" xlink:to="us-gaap_EmployeeRelatedLiabilitiesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Related Liabilities Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccruedProfessionalFeesCurrent" xlink:type="locator" xlink:label="us-gaap_AccruedProfessionalFeesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccruedProfessionalFeesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Legal and professional expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedProfessionalFeesCurrent" xlink:to="us-gaap_AccruedProfessionalFeesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccruedProfessionalFeesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Professional Fees Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease liabilities - short term</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiabilityCurrent" xlink:to="us-gaap_OperatingLeaseLiabilityCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liability Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:type="locator" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other accrued expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAccruedLiabilitiesCurrent" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Other Accrued Liabilities Current</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AbbVieIrelandUnlimitedCompanyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">AbbVie</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AmgenIncMember" xlink:type="locator" xlink:label="ctmx_AmgenIncMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AmgenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amgen Inc.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AmgenIncMember" xlink:to="ctmx_AmgenIncMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AmgenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Amgen</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AmgenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amgen Inc [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ImmunoGenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">ImmunoGen</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PfizerIncMember" xlink:type="locator" xlink:label="ctmx_PfizerIncMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PfizerIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Pfizer Inc.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PfizerIncMember" xlink:to="ctmx_PfizerIncMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PfizerIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Pfizer</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PfizerIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Pfizer Inc [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:type="locator" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Revenues" xlink:type="locator" xlink:label="us-gaap_Revenues" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Revenues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_Revenues_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenues</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfCollaborationAgreements" xlink:type="locator" xlink:label="ctmx_NumberOfCollaborationAgreements" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfCollaborationAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of collaboration agreements.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfCollaborationAgreements" xlink:to="ctmx_NumberOfCollaborationAgreements_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts" xlink:type="locator" xlink:label="ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of net Income or net losses related to development costs.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts" xlink:to="ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:type="locator" xlink:label="us-gaap_TypeOfArrangementAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangement and Arrangement Other than Collaborative</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_TypeOfArrangementAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Type Of Arrangement [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="locator" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangement and Arrangement Other than Collaborative</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Arrangements And Nonarrangement Transactions [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollaborativeArrangementMember" xlink:type="locator" xlink:label="us-gaap_CollaborativeArrangementMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CollaborativeArrangementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaborative Arrangement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CollaborativeArrangementMember" xlink:to="us-gaap_CollaborativeArrangementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CollaborativeArrangementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RangeAxis" xlink:to="srt_RangeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Range [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_RangeMember" xlink:to="srt_RangeMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_RangeMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Range [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:label xml:lang="en-US" xlink:label="srt_MaximumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MaximumMember" xlink:to="srt_MaximumMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_MaximumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Maximum [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:label xml:lang="en-US" xlink:label="srt_MinimumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_MinimumMember" xlink:to="srt_MinimumMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_MinimumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Minimum [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_StatementGeographicalAxis" xlink:type="locator" xlink:label="srt_StatementGeographicalAxis" />
    <link:label xml:lang="en-US" xlink:label="srt_StatementGeographicalAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Geographical</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_StatementGeographicalAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_StatementGeographicalAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Statement Geographical [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_SegmentGeographicalDomain" xlink:type="locator" xlink:label="srt_SegmentGeographicalDomain" />
    <link:label xml:lang="en-US" xlink:label="srt_SegmentGeographicalDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Geographical</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_SegmentGeographicalDomain" xlink:to="srt_SegmentGeographicalDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_SegmentGeographicalDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Segment Geographical [Domain]</link:label>
    <link:loc xlink:href="https://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_US" xlink:type="locator" xlink:label="country_US" />
    <link:label xml:lang="en-US" xlink:label="country_US_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">U.S</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="country_US" xlink:to="country_US_lbl" />
    <link:label xml:lang="en-US" xlink:label="country_US_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">UNITED STATES</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_CD71AgreementMember" xlink:type="locator" xlink:label="ctmx_CD71AgreementMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CD71AgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">CD 71 agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_CD71AgreementMember" xlink:to="ctmx_CD71AgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CD71AgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">CD71 Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CD71AgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">C D71 Agreement [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SeattleGeneticsAgreementMember" xlink:type="locator" xlink:label="ctmx_SeattleGeneticsAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SeattleGeneticsAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Seattle genetics agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SeattleGeneticsAgreementMember" xlink:to="ctmx_SeattleGeneticsAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SeattleGeneticsAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Seattle Genetics Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SeattleGeneticsAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Seattle Genetics Agreement [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_DiscoveryAgreementMember" xlink:type="locator" xlink:label="ctmx_DiscoveryAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DiscoveryAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Discovery agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_DiscoveryAgreementMember" xlink:to="ctmx_DiscoveryAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DiscoveryAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Discovery Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DiscoveryAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Discovery Agreement [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContingentConsiderationByTypeAxis" xlink:type="locator" xlink:label="us-gaap_ContingentConsiderationByTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContingentConsiderationByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent Consideration by Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContingentConsiderationByTypeAxis" xlink:to="us-gaap_ContingentConsiderationByTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContingentConsiderationByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Consideration By Type [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain" xlink:type="locator" xlink:label="us-gaap_ContingentConsiderationTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContingentConsiderationTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent Consideration Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContingentConsiderationTypeDomain" xlink:to="us-gaap_ContingentConsiderationTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContingentConsiderationTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Consideration Type [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember" xlink:type="locator" xlink:label="ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Development regulatory and commercial milestone payments.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember" xlink:to="ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Development, Regulatory and Commercial Milestone Payments</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Development Regulatory And Commercial Milestone Payments [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:label xml:lang="en-US" xlink:label="srt_ProductOrServiceAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Product and Service</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductOrServiceAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_ProductOrServiceAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Product Or Service [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:label xml:lang="en-US" xlink:label="srt_ProductsAndServicesDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Product and Service</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="srt_ProductsAndServicesDomain" xlink:to="srt_ProductsAndServicesDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="srt_ProductsAndServicesDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Products And Services [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SecondTargetMember" xlink:type="locator" xlink:label="ctmx_SecondTargetMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SecondTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Second target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SecondTargetMember" xlink:to="ctmx_SecondTargetMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SecondTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Second Target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SecondTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Second Target [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LicenseAgreementMember" xlink:type="locator" xlink:label="ctmx_LicenseAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LicenseAgreementMember" xlink:to="ctmx_LicenseAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Arrangement Contract To Perform For Others By Type [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Arrangement Contract To Perform For Others Type [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_RegentsOfTheUniversityOfCaliforniaMember" xlink:type="locator" xlink:label="ctmx_RegentsOfTheUniversityOfCaliforniaMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_RegentsOfTheUniversityOfCaliforniaMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Regents of the university of California.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_RegentsOfTheUniversityOfCaliforniaMember" xlink:to="ctmx_RegentsOfTheUniversityOfCaliforniaMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_RegentsOfTheUniversityOfCaliforniaMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">UC Regents</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_RegentsOfTheUniversityOfCaliforniaMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Regents Of The University Of California [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_UniversityOfCaliforniaSantaBarbaraMember" xlink:type="locator" xlink:label="ctmx_UniversityOfCaliforniaSantaBarbaraMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_UniversityOfCaliforniaSantaBarbaraMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">University of California, Santa Barbara.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_UniversityOfCaliforniaSantaBarbaraMember" xlink:to="ctmx_UniversityOfCaliforniaSantaBarbaraMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_UniversityOfCaliforniaSantaBarbaraMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">UCSB</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_UniversityOfCaliforniaSantaBarbaraMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">University Of California Santa Barbara [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfCollaborationAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of collaboration agreements</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfCollaborationAgreements_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Collaboration Agreements</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of net profits or net losses related to development costs</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Net Income Or Net Losses Related To Development Costs</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" xlink:type="locator" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contingent payments receivable upon achieving development, regulatory and commercial milestones.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" xlink:to="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentPaymentsReceivableProfitSplitOnSales" xlink:type="locator" xlink:label="ctmx_ContingentPaymentsReceivableProfitSplitOnSales" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableProfitSplitOnSales_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contingent payments receivable profit split on sales.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentPaymentsReceivableProfitSplitOnSales" xlink:to="ctmx_ContingentPaymentsReceivableProfitSplitOnSales_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod" xlink:type="locator" xlink:label="ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestone payments received from revenue recognized during period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod" xlink:to="ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PaymentsOfSublicenseFees" xlink:type="locator" xlink:label="ctmx_PaymentsOfSublicenseFees" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PaymentsOfSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Payments of sublicense fees.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PaymentsOfSublicenseFees" xlink:to="ctmx_PaymentsOfSublicenseFees_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromCollaborators" xlink:type="locator" xlink:label="us-gaap_ProceedsFromCollaborators" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromCollaborators_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront payment received</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromCollaborators" xlink:to="us-gaap_ProceedsFromCollaborators_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromCollaborators_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Collaborators</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent payments receivable upon achieving development, regulatory and commercial milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payments Receivable Upon Achieving Development Regulatory And Commercial Milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableProfitSplitOnSales_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Profit split on U.S. sales and royalties on ex U.S. sales</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableProfitSplitOnSales_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payments Receivable Profit Split On Sales</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestone payment received</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestone Payments Received From Revenue Recognized During Period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PaymentsOfSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublicense fees paid</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PaymentsOfSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments Of Sublicense Fees</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfTargets" xlink:type="locator" xlink:label="ctmx_NumberOfTargets" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfTargets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of targets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfTargets" xlink:to="ctmx_NumberOfTargets_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfTargetsSelected" xlink:type="locator" xlink:label="ctmx_NumberOfTargetsSelected" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfTargetsSelected_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of targets selected.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfTargetsSelected" xlink:to="ctmx_NumberOfTargetsSelected_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfTargets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of targets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfTargets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Targets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfTargetsSelected_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of targets selected</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfTargetsSelected_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Targets Selected</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentMilestonePaymentsReceivable" xlink:type="locator" xlink:label="ctmx_ContingentMilestonePaymentsReceivable" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentMilestonePaymentsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Future contingent milestone payment receivable.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentMilestonePaymentsReceivable" xlink:to="ctmx_ContingentMilestonePaymentsReceivable_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MilestonePaymentReceived" xlink:type="locator" xlink:label="ctmx_MilestonePaymentReceived" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestone payment received.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MilestonePaymentReceived" xlink:to="ctmx_MilestonePaymentReceived_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestone payments received</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentReceived_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestone Payment Received</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentMilestonePaymentsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent milestone payments receivable</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentMilestonePaymentsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Milestone Payments Receivable</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AggregateCollaborationTransactionAmount" xlink:type="locator" xlink:label="ctmx_AggregateCollaborationTransactionAmount" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AggregateCollaborationTransactionAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Aggregate collaboration transaction amount.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AggregateCollaborationTransactionAmount" xlink:to="ctmx_AggregateCollaborationTransactionAmount_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EstimatedSublicenseFees" xlink:type="locator" xlink:label="ctmx_EstimatedSublicenseFees" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Estimated sublicense fees.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EstimatedSublicenseFees" xlink:to="ctmx_EstimatedSublicenseFees_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfAccountingUnits" xlink:type="locator" xlink:label="ctmx_NumberOfAccountingUnits" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAccountingUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of accounting units.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfAccountingUnits" xlink:to="ctmx_NumberOfAccountingUnits_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MilestonePaymentsReceivable" xlink:type="locator" xlink:label="ctmx_MilestonePaymentsReceivable" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestone payments receivable.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MilestonePaymentsReceivable" xlink:to="ctmx_MilestonePaymentsReceivable_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AggregateCollaborationTransactionAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total transaction price</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AggregateCollaborationTransactionAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Aggregate Collaboration Transaction Amount</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated sublicense fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimated Sublicense Fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAccountingUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of accounting units</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAccountingUnits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Accounting Units</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestone payment received</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentsReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestone Payments Receivable</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_RevenueAdjustmentOfMilestonePaymentRecognized" xlink:type="locator" xlink:label="ctmx_RevenueAdjustmentOfMilestonePaymentRecognized" />
    <link:label xml:lang="en-US" xlink:label="ctmx_RevenueAdjustmentOfMilestonePaymentRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Revenue adjustment of milestone payment recognized.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_RevenueAdjustmentOfMilestonePaymentRecognized" xlink:to="ctmx_RevenueAdjustmentOfMilestonePaymentRecognized_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_RevenueAdjustmentOfMilestonePaymentRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue adjustment of milestone payment recognized</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_RevenueAdjustmentOfMilestonePaymentRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Adjustment Of Milestone Payment Recognized</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds" xlink:type="locator" xlink:label="ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License payment percentage equivalence to upfront and milestone proceeds.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds" xlink:to="ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License payment percentage</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Payment Percentage Equivalence To Upfront And Milestone Proceeds</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis" xlink:type="locator" xlink:label="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis" xlink:to="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Start Date [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1" xlink:type="locator" xlink:label="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue recognition upon performance obligation, service period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1" xlink:to="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Remaining Performance Obligation Expected Timing Of Satisfaction Period1</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EstimatedResearchServicePeriod" xlink:type="locator" xlink:label="ctmx_EstimatedResearchServicePeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedResearchServicePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Estimated research service period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EstimatedResearchServicePeriod" xlink:to="ctmx_EstimatedResearchServicePeriod_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation" xlink:type="locator" xlink:label="us-gaap_RevenueRemainingPerformanceObligation" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue recognition upon performance obligation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRemainingPerformanceObligation" xlink:to="us-gaap_RevenueRemainingPerformanceObligation_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueRemainingPerformanceObligation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue Remaining Performance Obligation</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedResearchServicePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated research service period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedResearchServicePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimated Research Service Period</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue recognized from collaborative arrangement</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContractWithCustomerLiability" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiability" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred revenue</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiability" xlink:to="us-gaap_ContractWithCustomerLiability_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContractWithCustomerAssetNet" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerAssetNet" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerAssetNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amount due from agreement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerAssetNet" xlink:to="us-gaap_ContractWithCustomerAssetNet_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerAssetNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Asset Net</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_CommonStockSharesIssuableUnderAgreement" xlink:type="locator" xlink:label="ctmx_CommonStockSharesIssuableUnderAgreement" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CommonStockSharesIssuableUnderAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock shares issuable under agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_CommonStockSharesIssuableUnderAgreement" xlink:to="ctmx_CommonStockSharesIssuableUnderAgreement_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare" xlink:type="locator" xlink:label="ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Period used to calculate weighted average price per share.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare" xlink:to="ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement" xlink:type="locator" xlink:label="ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Lock-up period for share transaction under collaboration and license agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement" xlink:to="ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EstimatedPremiumOnIssuanceOfShares" xlink:type="locator" xlink:label="ctmx_EstimatedPremiumOnIssuanceOfShares" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedPremiumOnIssuanceOfShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Estimated premium on issuance of shares.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EstimatedPremiumOnIssuanceOfShares" xlink:to="ctmx_EstimatedPremiumOnIssuanceOfShares_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_CollaborationAndLicenseAgreementMember" xlink:type="locator" xlink:label="ctmx_CollaborationAndLicenseAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CollaborationAndLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaboration and license agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_CollaborationAndLicenseAgreementMember" xlink:to="ctmx_CollaborationAndLicenseAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CollaborationAndLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaboration and License Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CollaborationAndLicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaboration And License Agreement [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AmgenIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amgen Inc</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EGFRProductsMember" xlink:type="locator" xlink:label="ctmx_EGFRProductsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EGFRProductsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">EGFR Products.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EGFRProductsMember" xlink:to="ctmx_EGFRProductsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EGFRProductsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">EGFR Products</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EGFRProductsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">E G F R Products [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SublicenseAgreementMember" xlink:type="locator" xlink:label="ctmx_SublicenseAgreementMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sublicense agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SublicenseAgreementMember" xlink:to="ctmx_SublicenseAgreementMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublicense Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseAgreementMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sublicense Agreement [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AmgenOtherProductsMember" xlink:type="locator" xlink:label="ctmx_AmgenOtherProductsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AmgenOtherProductsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amgen other products.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AmgenOtherProductsMember" xlink:to="ctmx_AmgenOtherProductsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AmgenOtherProductsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amgen Other Products</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AmgenOtherProductsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amgen Other Products [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CommonStockSharesIssuableUnderAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock, shares issuable under agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CommonStockSharesIssuableUnderAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Shares Issuable Under Agreement</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharePrice" xlink:type="locator" xlink:label="us-gaap_SharePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares issuable under agreement, price per share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharePrice" xlink:to="us-gaap_SharePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Price</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock, value of shares issued in connection with agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Period used to calculate weighted average price per share</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Period Used To Calculate Weighted Average Price Per Share</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lock-up period for share disposal</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lock Up Period For Share Transaction Under Collaboration And License Agreement</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedPremiumOnIssuanceOfShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated premium on the stock sold</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedPremiumOnIssuanceOfShares_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimated Premium On Issuance Of Shares</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ProfitShareUponExerciseOfCoDevelopmentOption" xlink:type="locator" xlink:label="ctmx_ProfitShareUponExerciseOfCoDevelopmentOption" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ProfitShareUponExerciseOfCoDevelopmentOption_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Profit share upon exercise of co-development option.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ProfitShareUponExerciseOfCoDevelopmentOption" xlink:to="ctmx_ProfitShareUponExerciseOfCoDevelopmentOption_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ProfitShareUponExerciseOfCoDevelopmentOption_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage share of profit and losses</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ProfitShareUponExerciseOfCoDevelopmentOption_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Profit Share Upon Exercise Of Co Development Option</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfAdditionalCollaborationTarget" xlink:type="locator" xlink:label="ctmx_NumberOfAdditionalCollaborationTarget" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAdditionalCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of additional collaboration target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfAdditionalCollaborationTarget" xlink:to="ctmx_NumberOfAdditionalCollaborationTarget_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAdditionalCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of additional collaboration target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAdditionalCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Additional Collaboration Target</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" xlink:type="locator" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contingent payments payable upon achieving development regulatory and commercial milestones.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" xlink:to="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent payments payable</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payments Payable Upon Achieving Development Regulatory And Commercial Milestones</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock" xlink:type="locator" xlink:label="ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Premium on issuance of shares allocated to common stock.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock" xlink:to="ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EstimatedFairValueOfProducts" xlink:type="locator" xlink:label="ctmx_EstimatedFairValueOfProducts" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFairValueOfProducts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Estimated fair value of products.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EstimatedFairValueOfProducts" xlink:to="ctmx_EstimatedFairValueOfProducts_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Portion of transaction price allocated to premium on sale of common stock</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Premium On Issuance Of Shares Allocated To Common Stock</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFairValueOfProducts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated fair value of products</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFairValueOfProducts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimated Fair Value Of Products</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod" xlink:type="locator" xlink:label="ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Estimated full time employee hours and research service period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod" xlink:to="ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated FTE hours to completion and research service period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimated Full Time Employee Hours And Research Service Period</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfOncologyTarget" xlink:type="locator" xlink:label="ctmx_NumberOfOncologyTarget" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfOncologyTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of oncology target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfOncologyTarget" xlink:to="ctmx_NumberOfOncologyTarget_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfCollaborationTarget" xlink:type="locator" xlink:label="ctmx_NumberOfCollaborationTarget" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of collaboration target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfCollaborationTarget" xlink:to="ctmx_NumberOfCollaborationTarget_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_CollaborationTargetResearchTerm" xlink:type="locator" xlink:label="ctmx_CollaborationTargetResearchTerm" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CollaborationTargetResearchTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Collaboration target research term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_CollaborationTargetResearchTerm" xlink:to="ctmx_CollaborationTargetResearchTerm_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PeriodOfNominationOfAdditionalTarget" xlink:type="locator" xlink:label="ctmx_PeriodOfNominationOfAdditionalTarget" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PeriodOfNominationOfAdditionalTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Period of nomination of additional target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PeriodOfNominationOfAdditionalTarget" xlink:to="ctmx_PeriodOfNominationOfAdditionalTarget_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ExtensionOfResearchTermForEachCollaborationTarget" xlink:type="locator" xlink:label="ctmx_ExtensionOfResearchTermForEachCollaborationTarget" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ExtensionOfResearchTermForEachCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Extension of research term for each collaboration target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ExtensionOfResearchTermForEachCollaborationTarget" xlink:to="ctmx_ExtensionOfResearchTermForEachCollaborationTarget_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes" xlink:type="locator" xlink:label="ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes" />
    <link:label xml:lang="en-US" xlink:label="ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Increments of extended collaboration target research times.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes" xlink:to="ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingAdditionalTargetsMember" xlink:type="locator" xlink:label="ctmx_AchievingAdditionalTargetsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingAdditionalTargetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving additional targets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingAdditionalTargetsMember" xlink:to="ctmx_AchievingAdditionalTargetsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingAdditionalTargetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Each Of Two Additional Targets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingAdditionalTargetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Additional Targets [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember" xlink:type="locator" xlink:label="ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achievement of development milestones for each research target program.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember" xlink:to="ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achievement Of Development Milestones For Each Research Target Program</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achievement Of Development Milestones For Each Research Target Program [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" xlink:type="locator" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achievement of development milestones if four research targets selected by counterparty.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" xlink:to="ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achievement Of Development Milestones If Four Research Targets Selected By Counterparty</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achievement Of Development Milestones If Four Research Targets Selected By Counterparty [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember" xlink:type="locator" xlink:label="ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Upon first commercial sale.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember" xlink:to="ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving First Commercial Sale In Various Territories</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving First Commercial Sale In Various Territories [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember" xlink:type="locator" xlink:label="ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving first commercial sale if four research targets selected by counterparty.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember" xlink:to="ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving First Commercial Sale If Four Research Targets Selected By Counterparty</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving First Commercial Sale If Four Research Targets Selected By Counterparty [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember" xlink:type="locator" xlink:label="ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving sales milestones for each research target program.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember" xlink:to="ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Sales Milestones For Each Research Target Program</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Sales Milestones For Each Research Target Program [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" xlink:type="locator" xlink:label="ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving sales milestones if four research targets selected by counterparty.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" xlink:to="ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Sales Milestones If Four Research Targets Selected By Counterparty</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Sales Milestones If Four Research Targets Selected By Counterparty [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PreClinicalCandidateMember" xlink:type="locator" xlink:label="ctmx_PreClinicalCandidateMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PreClinicalCandidateMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Pre clinical candidate.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PreClinicalCandidateMember" xlink:to="ctmx_PreClinicalCandidateMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PreClinicalCandidateMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pre Clinical Candidate</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PreClinicalCandidateMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Pre Clinical Candidate [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_DrugApplicationForCTLA4Member" xlink:type="locator" xlink:label="ctmx_DrugApplicationForCTLA4Member" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DrugApplicationForCTLA4Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Drug application for CTLA-4.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_DrugApplicationForCTLA4Member" xlink:to="ctmx_DrugApplicationForCTLA4Member_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DrugApplicationForCTLA4Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">New Drug Application for CTLA-4</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DrugApplicationForCTLA4Member_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Drug Application For C T L A4 [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember" xlink:type="locator" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achievement of development milestones if eight research targets selected by counterparty.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember" xlink:to="ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achievement of Development Milestones if Eight Research Targets Selected by Counterparty</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achievement Of Development Milestones If Eight Research Targets Selected By Counterparty [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember" xlink:type="locator" xlink:label="ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving eight targets selected for first product modality.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember" xlink:to="ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Eight Targets Selected for the First Product Modality</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Eight Targets Selected For First Product Modality [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember" xlink:type="locator" xlink:label="ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving sales milestones if eight research targets selected for first product modality.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember" xlink:to="ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Sales Milestones if Eight Research Targets Selected for First Product Modality</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Sales Milestones If Eight Research Targets Selected For First Product Modality [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingDevelopmentMilestonePaymentsMember" xlink:type="locator" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving development milestone payments.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingDevelopmentMilestonePaymentsMember" xlink:to="ctmx_AchievingDevelopmentMilestonePaymentsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Development Milestone Payments</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Development Milestone Payments [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember" xlink:type="locator" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving development milestone payment if eight research targets are selected for second product modality.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember" xlink:to="ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Development Milestone Payment if Eight Targets are Selected for Second Product Modality</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Development Milestone Payment If Eight Research Targets Are Selected For Second Product Modality [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember" xlink:type="locator" xlink:label="ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestone payments for the first commercial sale in various territories for up to three indications.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember" xlink:to="ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Milestone Payments for First Commercial Sale in Various Territories for Up to Three Indication</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Milestone Payments For First Commercial Sale In Various Territories For Up To Three Indications [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" xlink:type="locator" xlink:label="ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving milestone payment if eight research target are selected for second product modality.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" xlink:to="ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Development Milestone Payment if Eight Targets are Selected for Second Product Modality</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Milestone Payment If Eight Research Target Are Selected For Second Product Modality [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingSalesMilestonePaymentsPerTargetMember" xlink:type="locator" xlink:label="ctmx_AchievingSalesMilestonePaymentsPerTargetMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonePaymentsPerTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving sales milestone payments per target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingSalesMilestonePaymentsPerTargetMember" xlink:to="ctmx_AchievingSalesMilestonePaymentsPerTargetMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonePaymentsPerTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Sales Milestone Payments Per Target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonePaymentsPerTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Sales Milestone Payments Per Target [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" xlink:type="locator" xlink:label="ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Achieving sales milestone payment if eight research target are selected for second product modality.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" xlink:to="ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Achieving Sales Milestone Payment if Eight Research Target are selected for Second Product Modality</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Achieving Sales Milestone Payment If Eight Research Target Are Selected For Second Product Modality [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ThirdAndFourthTargetsMember" xlink:type="locator" xlink:label="ctmx_ThirdAndFourthTargetsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ThirdAndFourthTargetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Third and fourth targets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ThirdAndFourthTargetsMember" xlink:to="ctmx_ThirdAndFourthTargetsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ThirdAndFourthTargetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Third And Fourth Immuno-Oncology Targets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ThirdAndFourthTargetsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Third And Fourth Targets [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfOncologyTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of oncology target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfOncologyTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Oncology Target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of collaboration target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Collaboration Target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CollaborationTargetResearchTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collaboration target research term</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CollaborationTargetResearchTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Collaboration Target Research Term</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersDescriptionAndTerms" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersDescriptionAndTerms" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersDescriptionAndTerms_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research terms</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersDescriptionAndTerms" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersDescriptionAndTerms_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersDescriptionAndTerms_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Arrangement Contract To Perform For Others Description And Terms</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PeriodOfNominationOfAdditionalTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Period of nomination of additional target from effective date</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PeriodOfNominationOfAdditionalTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Period Of Nomination Of Additional Target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ExtensionOfResearchTermForEachCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Extension of research term for each collaboration target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ExtensionOfResearchTermForEachCollaborationTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Extension Of Research Term For Each Collaboration Target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Times of increments for extended collaboration target research time</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Increments Of Extended Collaboration Target Research Times</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfResearchTargetsSelected" xlink:type="locator" xlink:label="ctmx_NumberOfResearchTargetsSelected" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfResearchTargetsSelected_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of research targets selected.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfResearchTargetsSelected" xlink:to="ctmx_NumberOfResearchTargetsSelected_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram" xlink:type="locator" xlink:label="ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of sales indicators for each research target program.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram" xlink:to="ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfResearchTargetsSelected_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of research targets selected</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfResearchTargetsSelected_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Research Targets Selected</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of sales indicators</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Sales Indicators For Each Research Target Program</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfNonOncologyTarget" xlink:type="locator" xlink:label="ctmx_NumberOfNonOncologyTarget" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfNonOncologyTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of non-oncology target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfNonOncologyTarget" xlink:to="ctmx_NumberOfNonOncologyTarget_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfNonOncologyTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of non-oncology target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfNonOncologyTarget_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Non Oncology Target</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ResearchAndDevelopmentServiceFees" xlink:type="locator" xlink:label="ctmx_ResearchAndDevelopmentServiceFees" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchAndDevelopmentServiceFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Research and development service fees.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ResearchAndDevelopmentServiceFees" xlink:to="ctmx_ResearchAndDevelopmentServiceFees_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EstimatedResearchServiceTerminationDate" xlink:type="locator" xlink:label="ctmx_EstimatedResearchServiceTerminationDate" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedResearchServiceTerminationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Estimated research service termination date.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EstimatedResearchServiceTerminationDate" xlink:to="ctmx_EstimatedResearchServiceTerminationDate_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchAndDevelopmentServiceFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront payment received</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchAndDevelopmentServiceFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Service Fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedResearchServiceTerminationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated research service termination date</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedResearchServiceTerminationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimated Research Service Termination Date</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_CashPaymentToExecuteAgreement" xlink:type="locator" xlink:label="ctmx_CashPaymentToExecuteAgreement" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CashPaymentToExecuteAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash payment to execute the agreement.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_CashPaymentToExecuteAgreement" xlink:to="ctmx_CashPaymentToExecuteAgreement_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LicenseAgreementTermsMember" xlink:type="locator" xlink:label="us-gaap_LicenseAgreementTermsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LicenseAgreementTermsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">CX-2009 License</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LicenseAgreementTermsMember" xlink:to="us-gaap_LicenseAgreementTermsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LicenseAgreementTermsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement Terms [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransactionTypeAxis" xlink:type="locator" xlink:label="us-gaap_TransactionTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TransactionTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Transaction Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TransactionTypeAxis" xlink:to="us-gaap_TransactionTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TransactionTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Transaction Type [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransactionDomain" xlink:type="locator" xlink:label="us-gaap_TransactionDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Transaction</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TransactionDomain" xlink:to="us-gaap_TransactionDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Transaction [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LicenseReceivablesMember" xlink:type="locator" xlink:label="ctmx_LicenseReceivablesMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseReceivablesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License receivables.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LicenseReceivablesMember" xlink:to="ctmx_LicenseReceivablesMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseReceivablesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Licenses Received</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseReceivablesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Receivables [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember" xlink:type="locator" xlink:label="ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Research services, joint research committee participation and technology improvements.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember" xlink:to="ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research Services, Joint Research Committee Participation and Technology Improvements</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research Services Joint Research Committee Participation And Technology Improvements [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CashPaymentToExecuteAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront cash payment</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CashPaymentToExecuteAgreement_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Payment To Execute Agreement</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MilestonesPaymentsMadeDuringPeriod" xlink:type="locator" xlink:label="ctmx_MilestonesPaymentsMadeDuringPeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonesPaymentsMadeDuringPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestones payments made during period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MilestonesPaymentsMadeDuringPeriod" xlink:to="ctmx_MilestonesPaymentsMadeDuringPeriod_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones" xlink:type="locator" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contingent payments receivable upon achieving development and regulatory milestones.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones" xlink:to="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones" xlink:type="locator" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Expected receivable from sales mile stone payments.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones" xlink:to="ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones" xlink:type="locator" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contingent payments payable upon achieving development and regulatory milestones.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones" xlink:to="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones" xlink:type="locator" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contingent payments payable upon achieving sales milestones.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones" xlink:to="ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MilestonePaymentPayable" xlink:type="locator" xlink:label="ctmx_MilestonePaymentPayable" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentPayable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestone payment payable.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MilestonePaymentPayable" xlink:to="ctmx_MilestonePaymentPayable_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent payments receivable upon achieving development and regulatory milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payments Receivable Upon Achieving Development And Regulatory Milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent payments receivable upon achieving sales milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payments Receivable Upon Achieving Sales Milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent payments payable upon achieving development and regulatory milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payments Payable Upon Achieving Development And Regulatory Milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contingent payments payable upon achieving sales milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contingent Payments Payable Upon Achieving Sales Milestones</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonesPaymentsMadeDuringPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestones payments made during period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonesPaymentsMadeDuringPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestones Payments Made During Period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentPayable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestone payments payable</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentPayable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestone Payment Payable</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Estimated total fair value consideration recorded as deferred revenue</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EstimatedFairValueOfAssetsAndServices" xlink:type="locator" xlink:label="ctmx_EstimatedFairValueOfAssetsAndServices" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFairValueOfAssetsAndServices_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Estimated fair value of assets and services.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EstimatedFairValueOfAssetsAndServices" xlink:to="ctmx_EstimatedFairValueOfAssetsAndServices_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFairValueOfAssetsAndServices_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated fair value of assets and services</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EstimatedFairValueOfAssetsAndServices_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Estimated Fair Value Of Assets And Services</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_OptionsExpirationDate" xlink:type="locator" xlink:label="ctmx_OptionsExpirationDate" />
    <link:label xml:lang="en-US" xlink:label="ctmx_OptionsExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Option expiration date.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_OptionsExpirationDate" xlink:to="ctmx_OptionsExpirationDate_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MDAndersonMember" xlink:type="locator" xlink:label="ctmx_MDAndersonMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MDAndersonMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">MD Anderson.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MDAndersonMember" xlink:to="ctmx_MDAndersonMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MDAndersonMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">MD Anderson</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MDAndersonMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">M D Anderson [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OptionsExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Option expiration date</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OptionsExpirationDate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Options Expiration Date</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfNominatedResearchTargets" xlink:type="locator" xlink:label="ctmx_NumberOfNominatedResearchTargets" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfNominatedResearchTargets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of nominated research targets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfNominatedResearchTargets" xlink:to="ctmx_NumberOfNominatedResearchTargets_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NumberOfAdditionalResearchTargetsWithNominationOption" xlink:type="locator" xlink:label="ctmx_NumberOfAdditionalResearchTargetsWithNominationOption" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAdditionalResearchTargetsWithNominationOption_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of additional research targets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NumberOfAdditionalResearchTargetsWithNominationOption" xlink:to="ctmx_NumberOfAdditionalResearchTargetsWithNominationOption_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContractWithCustomerLiabilityAdditions" xlink:type="locator" xlink:label="ctmx_ContractWithCustomerLiabilityAdditions" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContractWithCustomerLiabilityAdditions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract with customer liability additions.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContractWithCustomerLiabilityAdditions" xlink:to="ctmx_ContractWithCustomerLiabilityAdditions_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PfizerIncMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pfizer Inc</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfNominatedResearchTargets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of research targets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfNominatedResearchTargets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Nominated Research Targets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAdditionalResearchTargetsWithNominationOption_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Nominated number of additional research targets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NumberOfAdditionalResearchTargetsWithNominationOption_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Additional Research Targets With Nomination Option</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContractWithCustomerLiabilityAdditions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional target as deferred revenue</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContractWithCustomerLiabilityAdditions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Additions</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AmortizationPeriodOfDeferredRevenue" xlink:type="locator" xlink:label="ctmx_AmortizationPeriodOfDeferredRevenue" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AmortizationPeriodOfDeferredRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amortization period of deferred revenue.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AmortizationPeriodOfDeferredRevenue" xlink:to="ctmx_AmortizationPeriodOfDeferredRevenue_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AmortizationPeriodOfDeferredRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjusted amortization period of deferred revenue</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AmortizationPeriodOfDeferredRevenue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Amortization Period Of Deferred Revenue</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueFromContractWithCustomerAbstract" xlink:type="locator" xlink:label="us-gaap_RevenueFromContractWithCustomerAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_RevenueFromContractWithCustomerAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Revenue From Contract With Customer [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueFromContractWithCustomerAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance at 12/31/2018</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additions</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress" xlink:to="us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInMeasureOfProgress_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Cumulative Catch Up Adjustment To Revenue Change In Measure Of Progress</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deductions</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:to="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Revenue Recognized</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance at 12/31/2019</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_FirstTargetMember" xlink:type="locator" xlink:label="ctmx_FirstTargetMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_FirstTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">First target.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_FirstTargetMember" xlink:to="ctmx_FirstTargetMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_FirstTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">First Target</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_FirstTargetMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">First Target [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContractWithCustomerLiabilityAdditions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Additions to deferred revenue</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ContractWithCustomerLiabilityRevenueRecognized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Deductions to deferred revenue recognized during the period</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear" xlink:type="locator" xlink:label="ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract with customer liability maturity month and year.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear" xlink:to="ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred revenue recognition maturity month and year</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Contract With Customer Liability Maturity Month And Year</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_RoyaltyObligationsFutureMinimumPaymentsDue" xlink:type="locator" xlink:label="ctmx_RoyaltyObligationsFutureMinimumPaymentsDue" />
    <link:label xml:lang="en-US" xlink:label="ctmx_RoyaltyObligationsFutureMinimumPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Royalty obligations future minimum payments due.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_RoyaltyObligationsFutureMinimumPaymentsDue" xlink:to="ctmx_RoyaltyObligationsFutureMinimumPaymentsDue_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LicenseTerminationPeriod" xlink:type="locator" xlink:label="ctmx_LicenseTerminationPeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseTerminationPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Period of time to terminate license after notice date.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LicenseTerminationPeriod" xlink:to="ctmx_LicenseTerminationPeriod_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Research And Development Arrangement Contract To Perform For Others [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable" xlink:to="us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Research And Development Arrangement Contract To Perform For Others [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement Location [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_IncomeStatementLocationDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement Location [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SublicenseAndMaintenanceFeesMember" xlink:type="locator" xlink:label="ctmx_SublicenseAndMaintenanceFeesMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseAndMaintenanceFeesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sublicense and maintenance fees.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SublicenseAndMaintenanceFeesMember" xlink:to="ctmx_SublicenseAndMaintenanceFeesMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseAndMaintenanceFeesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublicense and Maintenance Fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseAndMaintenanceFeesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sublicense And Maintenance Fees [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AbbVieMember" xlink:type="locator" xlink:label="ctmx_AbbVieMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AbbVieMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">AbbVie .</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AbbVieMember" xlink:to="ctmx_AbbVieMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AbbVieMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">AbbVie</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AbbVieMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Abb Vie [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreement [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Arrangement Contract To Perform For Others [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_RoyaltyObligationsFutureMinimumPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Annual minimum royalty obligations</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_RoyaltyObligationsFutureMinimumPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Royalty Obligations Future Minimum Payments Due</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseTerminationPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License termination period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicenseTerminationPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Termination Period</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PaymentOfUpfrontFees" xlink:type="locator" xlink:label="ctmx_PaymentOfUpfrontFees" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PaymentOfUpfrontFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Payment of upfront fees.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PaymentOfUpfrontFees" xlink:to="ctmx_PaymentOfUpfrontFees_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AnnualLicenseMaintenanceFees" xlink:type="locator" xlink:label="ctmx_AnnualLicenseMaintenanceFees" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AnnualLicenseMaintenanceFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Annual license maintenance fees</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AnnualLicenseMaintenanceFees" xlink:to="ctmx_AnnualLicenseMaintenanceFees_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_LicensePaymentTerm" xlink:type="locator" xlink:label="ctmx_LicensePaymentTerm" />
    <link:label xml:lang="en-US" xlink:label="ctmx_LicensePaymentTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">License payment term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_LicensePaymentTerm" xlink:to="ctmx_LicensePaymentTerm_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PercentageOfRemainingMaintenanceFeesOutstanding" xlink:type="locator" xlink:label="ctmx_PercentageOfRemainingMaintenanceFeesOutstanding" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfRemainingMaintenanceFeesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of remaining maintenance fees outstanding.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PercentageOfRemainingMaintenanceFeesOutstanding" xlink:to="ctmx_PercentageOfRemainingMaintenanceFeesOutstanding_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_FairValueOfCommonStockIssued" xlink:type="locator" xlink:label="ctmx_FairValueOfCommonStockIssued" />
    <link:label xml:lang="en-US" xlink:label="ctmx_FairValueOfCommonStockIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair value of common stock issued.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_FairValueOfCommonStockIssued" xlink:to="ctmx_FairValueOfCommonStockIssued_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharesIssuedPricePerShare" xlink:type="locator" xlink:label="us-gaap_SharesIssuedPricePerShare" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssuedPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair value of common stock price per share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesIssuedPricePerShare" xlink:to="us-gaap_SharesIssuedPricePerShare_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssuedPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Shares Issued Price Per Share</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PaymentOfUpfrontFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Payment of upfront fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PaymentOfUpfrontFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payment Of Upfront Fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AnnualLicenseMaintenanceFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Annual license maintenance fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AnnualLicenseMaintenanceFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Annual License Maintenance Fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicensePaymentTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License payment term</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LicensePaymentTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">License Payment Term</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfRemainingMaintenanceFeesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of remaining maintenance fees outstanding</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfRemainingMaintenanceFeesOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Remaining Maintenance Fees Outstanding</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_FairValueOfCommonStockIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair value of common stock issued</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_FairValueOfCommonStockIssued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Of Common Stock Issued</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_AdditionalSublicenseFees" xlink:type="locator" xlink:label="ctmx_AdditionalSublicenseFees" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AdditionalSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Additional sublicense fees.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_AdditionalSublicenseFees" xlink:to="ctmx_AdditionalSublicenseFees_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MilestonePaymentReceivable" xlink:type="locator" xlink:label="ctmx_MilestonePaymentReceivable" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Milestone payment receivable.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MilestonePaymentReceivable" xlink:to="ctmx_MilestonePaymentReceivable_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_AdditionalSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional sublicense fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_AdditionalSublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Additional Sublicense Fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Milestone payment receivable</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MilestonePaymentReceivable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Milestone Payment Receivable</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SublicenseFees" xlink:type="locator" xlink:label="ctmx_SublicenseFees" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Sublicense fees.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SublicenseFees" xlink:to="ctmx_SublicenseFees_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublicense fees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SublicenseFees_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sublicense Fees</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Accrued liabilities</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_UpfrontLicensePayment" xlink:type="locator" xlink:label="ctmx_UpfrontLicensePayment" />
    <link:label xml:lang="en-US" xlink:label="ctmx_UpfrontLicensePayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Upfront license payment.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_UpfrontLicensePayment" xlink:to="ctmx_UpfrontLicensePayment_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_UpfrontLicensePayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Upfront license payment</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_UpfrontLicensePayment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Upfront License Payment</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfOperatingLeasedAssetsTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfOperatingLeasedAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Operating Leased Assets [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:to="us-gaap_ScheduleOfOperatingLeasedAssetsTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfOperatingLeasedAssetsTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Operating Leased Assets [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LeaseAgreementsMember" xlink:type="locator" xlink:label="us-gaap_LeaseAgreementsMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseAgreementsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">New Lease Agreement</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseAgreementsMember" xlink:to="us-gaap_LeaseAgreementsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseAgreementsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Agreements [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LeaseArrangementTypeAxis" xlink:type="locator" xlink:label="us-gaap_LeaseArrangementTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease Arrangement, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseArrangementTypeAxis" xlink:to="us-gaap_LeaseArrangementTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Arrangement Type [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LeaseArrangementTypeDomain" xlink:type="locator" xlink:label="us-gaap_LeaseArrangementTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease Arrangement, Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseArrangementTypeDomain" xlink:to="us-gaap_LeaseArrangementTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LeaseArrangementTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lease Arrangement Type [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_FirstYearOfLeaseTermMember" xlink:type="locator" xlink:label="ctmx_FirstYearOfLeaseTermMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_FirstYearOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">First year of lease term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_FirstYearOfLeaseTermMember" xlink:to="ctmx_FirstYearOfLeaseTermMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_FirstYearOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">First year of lease term</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_FirstYearOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">First Year Of Lease Term [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SecondTwelveMonthsOfLeaseTermMember" xlink:type="locator" xlink:label="ctmx_SecondTwelveMonthsOfLeaseTermMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SecondTwelveMonthsOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Second twelve months of lease term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SecondTwelveMonthsOfLeaseTermMember" xlink:to="ctmx_SecondTwelveMonthsOfLeaseTermMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SecondTwelveMonthsOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Second twelve months of lease term</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SecondTwelveMonthsOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Second Twelve Months Of Lease Term [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_TenthYearOfLeaseTermMember" xlink:type="locator" xlink:label="ctmx_TenthYearOfLeaseTermMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_TenthYearOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Tenth year of lease term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_TenthYearOfLeaseTermMember" xlink:to="ctmx_TenthYearOfLeaseTermMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_TenthYearOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tenth year of lease term</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_TenthYearOfLeaseTermMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tenth Year Of Lease Term [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:type="locator" xlink:label="us-gaap_CreditFacilityAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CreditFacilityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Credit Facility</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CreditFacilityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Credit Facility [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:type="locator" xlink:label="us-gaap_CreditFacilityDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CreditFacilityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Credit Facility</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_CreditFacilityDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CreditFacilityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Credit Facility [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LetterOfCreditMember" xlink:type="locator" xlink:label="us-gaap_LetterOfCreditMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LetterOfCreditMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Letter of Credit</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LetterOfCreditMember" xlink:to="us-gaap_LetterOfCreditMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LetterOfCreditMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Letter Of Credit [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeasedAssetsLineItems" xlink:type="locator" xlink:label="us-gaap_OperatingLeasedAssetsLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasedAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Leased Assets [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasedAssetsLineItems" xlink:to="us-gaap_OperatingLeasedAssetsLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasedAssetsLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leased Assets [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AreaOfLand" xlink:type="locator" xlink:label="us-gaap_AreaOfLand" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AreaOfLand_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Area of rentable office and laboratory space</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AreaOfLand" xlink:to="us-gaap_AreaOfLand_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AreaOfLand_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Area Of Land</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseDescription" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseDescription" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease term description</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseDescription" xlink:to="us-gaap_LesseeOperatingLeaseDescription_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseDescription_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Description</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Initial lease term</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseTermOfContract" xlink:to="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Term Of Contract</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseRenewalTerm" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseRenewalTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Extended lease term</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:to="us-gaap_LesseeOperatingLeaseRenewalTerm_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseRenewalTerm_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Renewal Term</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_OperatingLeasesRentExpenseAnnualBaseRent" xlink:type="locator" xlink:label="ctmx_OperatingLeasesRentExpenseAnnualBaseRent" />
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLeasesRentExpenseAnnualBaseRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating leases rent expense annual base rent.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_OperatingLeasesRentExpenseAnnualBaseRent" xlink:to="ctmx_OperatingLeasesRentExpenseAnnualBaseRent_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_MaximumImprovementAllowance" xlink:type="locator" xlink:label="ctmx_MaximumImprovementAllowance" />
    <link:label xml:lang="en-US" xlink:label="ctmx_MaximumImprovementAllowance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum improvement allowance.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_MaximumImprovementAllowance" xlink:to="ctmx_MaximumImprovementAllowance_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ImprovementAllowanceFromRecoverableRent" xlink:type="locator" xlink:label="ctmx_ImprovementAllowanceFromRecoverableRent" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ImprovementAllowanceFromRecoverableRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Improvement allowance from recoverable rent.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ImprovementAllowanceFromRecoverableRent" xlink:to="ctmx_ImprovementAllowanceFromRecoverableRent_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLeasesRentExpenseAnnualBaseRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Annual lease rent</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLeasesRentExpenseAnnualBaseRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Leases Rent Expense Annual Base Rent</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MaximumImprovementAllowance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum one-time improvement allowance</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_MaximumImprovementAllowance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Maximum Improvement Allowance</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ImprovementAllowanceFromRecoverableRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Improvement allowance from recoverable rent</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ImprovementAllowanceFromRecoverableRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Improvement Allowance From Recoverable Rent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:type="locator" xlink:label="us-gaap_LettersOfCreditOutstandingAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LettersOfCreditOutstandingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Letter of credit outstanding, amount</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LettersOfCreditOutstandingAmount" xlink:to="us-gaap_LettersOfCreditOutstandingAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LettersOfCreditOutstandingAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Letters Of Credit Outstanding Amount</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseExpense" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Rent expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseExpense" xlink:to="us-gaap_OperatingLeaseExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Expense</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract" xlink:type="locator" xlink:label="ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid for amounts included in measurement of lease liabilities.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract" xlink:to="ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract" xlink:type="locator" xlink:label="ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract" />
    <link:label xml:lang="en-US" xlink:label="ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Supplemental balance sheet information related to leases.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract" xlink:to="ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_WeightedAverageRemainingLeaseTermAbstract" xlink:type="locator" xlink:label="ctmx_WeightedAverageRemainingLeaseTermAbstract" />
    <link:label xml:lang="en-US" xlink:label="ctmx_WeightedAverageRemainingLeaseTermAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Weighted average remaining lease term.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_WeightedAverageRemainingLeaseTermAbstract" xlink:to="ctmx_WeightedAverageRemainingLeaseTermAbstract_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_WeightedAverageDiscountRateAbstract" xlink:type="locator" xlink:label="ctmx_WeightedAverageDiscountRateAbstract" />
    <link:label xml:lang="en-US" xlink:label="ctmx_WeightedAverageDiscountRateAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Weighted average discount rate.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_WeightedAverageDiscountRateAbstract" xlink:to="ctmx_WeightedAverageDiscountRateAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for amounts included in the measurement of lease liabilities</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid For Amounts Included In Measurement Of Lease Liabilities [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeasePayments" xlink:type="locator" xlink:label="us-gaap_OperatingLeasePayments" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating cash flows from operating leases</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasePayments" xlink:to="us-gaap_OperatingLeasePayments_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Payments</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental balance sheet information related to leases:</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Balance Sheet Information Related To Leases [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Operating lease right-of-use assets</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Current operating lease liabilities</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityNoncurrent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Non-current operating lease liabilities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList" xlink:to="us-gaap_OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liability Current Statement Of Financial Position Extensible List</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total operating lease liabilities</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_WeightedAverageRemainingLeaseTermAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted-average remaining lease term (in years)</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_WeightedAverageRemainingLeaseTermAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Remaining Lease Term [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:to="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Weighted Average Remaining Lease Term1</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_WeightedAverageDiscountRateAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted-average discount rate</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_WeightedAverageDiscountRateAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Discount Rate [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:to="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Weighted Average Discount Rate Percent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract" xlink:type="locator" xlink:label="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maturity of operating lease liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract" xlink:to="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liabilities Payments Due [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Next Twelve Months</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2021</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Year Two</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2022</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Year Three</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2023</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Year Four</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LesseeOperatingLeaseLiabilityPaymentsDueYearFiveAndThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2024 and beyond</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_LesseeOperatingLeaseLiabilityPaymentsDueYearFiveAndThereafter_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due Year Five And Thereafter</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total lease payments</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Payments Due</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:type="locator" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less imputed interest</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:to="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Lessee Operating Lease Liability Undiscounted Excess Amount</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Present value of lease liabilities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfStockByClassTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfStockByClassTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Stock By Class [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfStockByClassTable" xlink:to="us-gaap_ScheduleOfStockByClassTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfStockByClassTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Stock By Class [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:type="locator" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsidiary Sale Of Stock [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:type="locator" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sale Of Stock Name Of Transaction [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_UnderwrittenPublicOfferingMember" xlink:type="locator" xlink:label="ctmx_UnderwrittenPublicOfferingMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_UnderwrittenPublicOfferingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Underwritten public offering.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_UnderwrittenPublicOfferingMember" xlink:to="ctmx_UnderwrittenPublicOfferingMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_UnderwrittenPublicOfferingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Underwritten Public Offering</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_UnderwrittenPublicOfferingMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Underwritten Public Offering [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OverAllotmentOptionMember" xlink:type="locator" xlink:label="us-gaap_OverAllotmentOptionMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OverAllotmentOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Underwriters</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OverAllotmentOptionMember" xlink:to="us-gaap_OverAllotmentOptionMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OverAllotmentOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Over Allotment Option [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:type="locator" xlink:label="us-gaap_ClassOfStockLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class Of Stock [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ClassOfStockLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Stock [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Preferred stock, shares authorized</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Preferred stock, par value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendsCommonStock" xlink:type="locator" xlink:label="us-gaap_DividendsCommonStock" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DividendsCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Dividends on common stock</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DividendsCommonStock" xlink:to="us-gaap_DividendsCommonStock_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DividendsCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Dividends Common Stock</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharesIssuedPricePerShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock price, per share</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel">Net proceeds from sale of common stock</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:type="locator" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Underwriting discounts and commissions and offering expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsOfStockIssuanceCosts" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Payments Of Stock Issuance Costs</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_StockOptionsIssuedAndOutstanding" xlink:type="locator" xlink:label="ctmx_StockOptionsIssuedAndOutstanding" />
    <link:label xml:lang="en-US" xlink:label="ctmx_StockOptionsIssuedAndOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock options issued and outstanding.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_StockOptionsIssuedAndOutstanding" xlink:to="ctmx_StockOptionsIssuedAndOutstanding_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share-based compensation arrangement by share-based payment award, number of shares available for future issuance under employee stock purchase plan.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_StockOptionsIssuedAndOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options issued and outstanding</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_StockOptionsIssuedAndOutstanding_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Stock Options Issued And Outstanding</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares available for future stock option grants</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares available for future employee stock purchase plan</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Future Issuance Under Employee Stock Purchase Plan</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:type="locator" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Capital Shares Reserved For Future Issuance</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award voting rights of common stock holding percentage.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PlanNameAxis" xlink:type="locator" xlink:label="us-gaap_PlanNameAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PlanNameDomain" xlink:type="locator" xlink:label="us-gaap_PlanNameDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PlanNameDomain" xlink:to="us-gaap_PlanNameDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Domain]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_TwoThousandFifteenStockIncentivePlanMember" xlink:type="locator" xlink:label="ctmx_TwoThousandFifteenStockIncentivePlanMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_TwoThousandFifteenStockIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand fifteen stock incentive plan.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_TwoThousandFifteenStockIncentivePlanMember" xlink:to="ctmx_TwoThousandFifteenStockIncentivePlanMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_TwoThousandFifteenStockIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2015 Plan</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_TwoThousandFifteenStockIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Fifteen Stock Incentive Plan [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_TwoThousandNineteenStockIncentivePlanMember" xlink:type="locator" xlink:label="ctmx_TwoThousandNineteenStockIncentivePlanMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_TwoThousandNineteenStockIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Two Thousand Nineteen Stock Incentive Plan Member.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_TwoThousandNineteenStockIncentivePlanMember" xlink:to="ctmx_TwoThousandNineteenStockIncentivePlanMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_TwoThousandNineteenStockIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2019 Plan</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_TwoThousandNineteenStockIncentivePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Nineteen Stock Incentive Plan [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_VestingAxis" xlink:type="locator" xlink:label="us-gaap_VestingAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VestingAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VestingAxis" xlink:to="us-gaap_VestingAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VestingAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Vesting [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_VestingDomain" xlink:type="locator" xlink:label="us-gaap_VestingDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VestingDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VestingDomain" xlink:to="us-gaap_VestingDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_VestingDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Vesting [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheOneMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheOneMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share Based Compensation Award Tranche One</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheOneMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheOneMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Award Tranche One [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheTwoMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheTwoMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting per Month After First Anniversary</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheTwoMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheTwoMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Award Tranche Two [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis" xlink:type="locator" xlink:label="us-gaap_AwardTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AwardTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Award Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_AwardTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AwardTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Award Type [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Award Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Award Type And Plan Name [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:type="locator" xlink:label="us-gaap_EmployeeStockOptionMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeStockOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employee Stock Option</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeStockOptionMember" xlink:to="us-gaap_EmployeeStockOptionMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeStockOptionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Stock Option [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EarlyExerciseOfEmployeeOptionsMember" xlink:type="locator" xlink:label="ctmx_EarlyExerciseOfEmployeeOptionsMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EarlyExerciseOfEmployeeOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Early exercise of employee options.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EarlyExerciseOfEmployeeOptionsMember" xlink:to="ctmx_EarlyExerciseOfEmployeeOptionsMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EarlyExerciseOfEmployeeOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Early Exercise of Employee Options</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EarlyExerciseOfEmployeeOptionsMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Early Exercise Of Employee Options [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EmployeeStockPurchasePlanMember" xlink:type="locator" xlink:label="ctmx_EmployeeStockPurchasePlanMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EmployeeStockPurchasePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Employee stock purchase plan.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EmployeeStockPurchasePlanMember" xlink:to="ctmx_EmployeeStockPurchasePlanMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EmployeeStockPurchasePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employee Stock Purchase Plan</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EmployeeStockPurchasePlanMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Stock Purchase Plan [Member]</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_NonEmployeesMember" xlink:type="locator" xlink:label="ctmx_NonEmployeesMember" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NonEmployeesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Non-Employees Member.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_NonEmployeesMember" xlink:to="ctmx_NonEmployeesMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_NonEmployeesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-employees</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_NonEmployeesMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Non Employees [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock, capital shares reserved for future issuance</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increase in number of shares available for issuance, as proportion of issued and outstanding shares of common stock, percentage</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Percentage Of Outstanding Stock Maximum</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock option expiration period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Expiration Period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employees holding voting rights of all classes of stock, percentage</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Voting Rights Of Common Stock Holding Percentage</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated fair value of the shares on the date of grant</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Purchase Price Of Common Stock Percent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options granted generally vest period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options granted generally vest percent</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Award Vesting Rights Percentage</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award number of shares available for grant authorized.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award number of shares available for grant grants in period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award number of shares available for grant exercises in period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award number of shares available for grant forfeitures in period.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award, number of shares available for grant.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options Available for Grant</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balances, beginning of the period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options authorized</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Authorized</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Options granted</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Grants In Period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options exercised</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Exercises In Period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options forfeited</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Forfeitures In Period</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balances, end of the period</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award options authorized.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of Options</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balances, beginning of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options authorized</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Authorized</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options granted</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Options exercised</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Options forfeited</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balances, end of the period</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options Exercisable, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options vested and expected to vest, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Number</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangements by share based payment award options authorized weighted average exercise price.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice" xlink:to="ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options Outstanding, Weighted-Average Exercise Price Per Share</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price Rollforward</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balances, beginning of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options granted</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options exercised</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options forfeited</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balances, end of the period</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options authorized</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangements By Share Based Payment Award Options Authorized Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options Exercisable, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options vested and expected to vest, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Exercise Price</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options Outstanding, Weighted- Average Remaining Contractual Life (years)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balances, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options Exercisable, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options vested and expected to vest, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term1</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" xlink:type="locator" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award options aggregate intrinsic value.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" xlink:to="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate Intrinsic Value</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Aggregate Intrinsic Value [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balances, end of the period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options Exercisable&#8212;December 31, 2019</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options vested and expected to vest&#8212;December 31, 2019</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Aggregate Intrinsic Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate intrinsic value of stock options exercised</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted average grant date fair value, options granted</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:type="locator" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrecognized compensation expense, options granted to employees</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Stock Options</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:type="locator" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Unrecognized stock-based compensation cost, period for recognition</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Period For Recognition1</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan maximum percentage of eligible compensation to purchase shares</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Maximum Employee Subscription Rate</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Number of shares issued during period</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:type="locator" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation expense</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AllocatedShareBasedCompensationExpense" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Allocated Share Based Compensation Expense</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:type="locator" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Unrecognized stock-based compensation cost</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Share Based Awards Other Than Options</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseMember" xlink:to="us-gaap_ResearchAndDevelopmentExpenseMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Expense [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:type="locator" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">General and administrative</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GeneralAndAdministrativeExpenseMember" xlink:to="us-gaap_GeneralAndAdministrativeExpenseMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">General And Administrative Expense [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationAbstract" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation expense:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationAbstract" xlink:to="us-gaap_ShareBasedCompensationAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation [Abstract]</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Stock-based compensation expense</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expected volatility, minimum</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate Minimum</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expected volatility, maximum</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate Maximum</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Risk-free interest rate, minimum</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate Minimum</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Risk-free interest rate, maximum</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate Maximum</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Dividend yield</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:type="locator" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expected term (in years)</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefitAbstract" xlink:type="locator" xlink:label="us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefitAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefitAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefitAbstract" xlink:to="us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefitAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefitAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Current Federal State And Local Tax Expense Benefit [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CurrentFederalTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_CurrentFederalTaxExpenseBenefit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentFederalTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CurrentFederalTaxExpenseBenefit" xlink:to="us-gaap_CurrentFederalTaxExpenseBenefit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentFederalTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Current Federal Tax Expense Benefit</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CurrentStateAndLocalTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_CurrentStateAndLocalTaxExpenseBenefit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentStateAndLocalTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CurrentStateAndLocalTaxExpenseBenefit" xlink:to="us-gaap_CurrentStateAndLocalTaxExpenseBenefit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentStateAndLocalTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Current State And Local Tax Expense Benefit</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CurrentIncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_CurrentIncomeTaxExpenseBenefit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CurrentIncomeTaxExpenseBenefit" xlink:to="us-gaap_CurrentIncomeTaxExpenseBenefit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_CurrentIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Current Income Tax Expense Benefit</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:type="locator" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred:</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income Tax Expense Benefit Continuing Operations [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredFederalIncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_DeferredFederalIncomeTaxExpenseBenefit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredFederalIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredFederalIncomeTaxExpenseBenefit" xlink:to="us-gaap_DeferredFederalIncomeTaxExpenseBenefit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredFederalIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Federal Income Tax Expense Benefit</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" xlink:to="us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred State And Local Income Tax Expense Benefit</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total deferred</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:to="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income Tax Expense Benefit</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Provision for (benefit from) income taxes</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation" xlink:type="locator" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Effective income tax rate reconciliation operating loss carry forward limitation.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation" xlink:to="ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments" xlink:type="locator" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments" />
    <link:label xml:lang="en-US" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Effective income tax rate reconciliation return to provision adjustments.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments" xlink:to="ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">U.S. federal taxes at statutory rate</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State tax, net of federal benefit</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation State And Local Income Taxes</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock compensation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax attributes subject to 382 limitation</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Operating Loss Carry Forward Limitation</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax credits</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Tax Credits</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in valuation allowance</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in deferreds due to rate change</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Return to provision adjustment</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Return To Provision Adjustments</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Other Adjustments</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:type="locator" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:to="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Continuing Operations</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_DeferredTaxAssetsLeaseLiability" xlink:type="locator" xlink:label="ctmx_DeferredTaxAssetsLeaseLiability" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DeferredTaxAssetsLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Deferred tax assets lease liability.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_DeferredTaxAssetsLeaseLiability" xlink:to="ctmx_DeferredTaxAssetsLeaseLiability_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_DeferredTaxLiabilitiesRightOfUseAssets" xlink:type="locator" xlink:label="ctmx_DeferredTaxLiabilitiesRightOfUseAssets" />
    <link:label xml:lang="en-US" xlink:label="ctmx_DeferredTaxLiabilitiesRightOfUseAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Deferred tax liabilities right of use assets.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_DeferredTaxLiabilitiesRightOfUseAssets" xlink:to="ctmx_DeferredTaxLiabilitiesRightOfUseAssets_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ComponentsOfDeferredTaxAssetsAndLiabilitiesAbstract" xlink:type="locator" xlink:label="us-gaap_ComponentsOfDeferredTaxAssetsAndLiabilitiesAbstract" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ComponentsOfDeferredTaxAssetsAndLiabilitiesAbstract_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Components Of Deferred Tax Assets And Liabilities [Abstract]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAndLiabilitiesAbstract" xlink:to="us-gaap_ComponentsOfDeferredTaxAssetsAndLiabilitiesAbstract_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net operating loss carryforwards</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Operating Loss Carryforwards</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development credits</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch" xlink:to="us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Tax Credit Carryforwards Research</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DeferredTaxAssetsLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease liability</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DeferredTaxAssetsLeaseLiability_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Lease Liability</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets" xlink:to="us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Goodwill And Intangible Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsDeferredIncome" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsDeferredIncome" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsDeferredIncome_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred revenue</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsDeferredIncome" xlink:to="us-gaap_DeferredTaxAssetsDeferredIncome_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsDeferredIncome_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Deferred Income</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDeferredRent" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDeferredRent" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDeferredRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accruals and deferred rent</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDeferredRent" xlink:to="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDeferredRent_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDeferredRent_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Deferred Rent</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based compensation</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost" xlink:to="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsOther" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsOther" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsOther_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOther" xlink:to="us-gaap_DeferredTaxAssetsOther_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsOther_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Other</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsGross" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsGross" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total gross deferred income tax assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsGross" xlink:to="us-gaap_DeferredTaxAssetsGross_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsGross_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Gross</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowance" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less: valuation allowance</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsValuationAllowance" xlink:to="us-gaap_DeferredTaxAssetsValuationAllowance_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Valuation Allowance</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxAssetsNet" xlink:type="locator" xlink:label="us-gaap_DeferredTaxAssetsNet" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred tax assets, net of valuation allowance</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsNet" xlink:to="us-gaap_DeferredTaxAssetsNet_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxAssetsNet_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Net</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Fixed assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment" xlink:to="us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities Property Plant And Equipment</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DeferredTaxLiabilitiesRightOfUseAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Right-of-use assets</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_DeferredTaxLiabilitiesRightOfUseAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities Right Of Use Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets" xlink:type="locator" xlink:label="us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Intangible assets</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets" xlink:to="us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities Goodwill And Intangible Assets</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxLiabilitiesPrepaidExpenses" xlink:type="locator" xlink:label="us-gaap_DeferredTaxLiabilitiesPrepaidExpenses" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesPrepaidExpenses_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Prepaid expenses</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxLiabilitiesPrepaidExpenses" xlink:to="us-gaap_DeferredTaxLiabilitiesPrepaidExpenses_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesPrepaidExpenses_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities Prepaid Expenses</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxLiabilitiesOther" xlink:type="locator" xlink:label="us-gaap_DeferredTaxLiabilitiesOther" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesOther_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxLiabilitiesOther" xlink:to="us-gaap_DeferredTaxLiabilitiesOther_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilitiesOther_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities Other</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilities" xlink:type="locator" xlink:label="us-gaap_DeferredIncomeTaxLiabilities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel">Deferred tax liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredIncomeTaxLiabilities" xlink:to="us-gaap_DeferredIncomeTaxLiabilities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredIncomeTaxLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income Tax Liabilities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredTaxLiabilities" xlink:type="locator" xlink:label="us-gaap_DeferredTaxLiabilities" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel">Net deferred income tax liabilities</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxLiabilities" xlink:to="us-gaap_DeferredTaxLiabilities_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DeferredTaxLiabilities_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxContingencyTable" xlink:type="locator" xlink:label="us-gaap_IncomeTaxContingencyTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxContingencyTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Contingency [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxContingencyTable" xlink:to="us-gaap_IncomeTaxContingencyTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxContingencyTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Contingency [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:type="locator" xlink:label="us-gaap_IncomeTaxAuthorityAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Authority</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxAuthorityAxis" xlink:to="us-gaap_IncomeTaxAuthorityAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Authority [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:type="locator" xlink:label="us-gaap_IncomeTaxAuthorityDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Authority</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxAuthorityDomain" xlink:to="us-gaap_IncomeTaxAuthorityDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxAuthorityDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Authority [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DomesticCountryMember" xlink:type="locator" xlink:label="us-gaap_DomesticCountryMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DomesticCountryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DomesticCountryMember" xlink:to="us-gaap_DomesticCountryMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DomesticCountryMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Domestic Country [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:type="locator" xlink:label="us-gaap_StateAndLocalJurisdictionMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StateAndLocalJurisdictionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StateAndLocalJurisdictionMember" xlink:to="us-gaap_StateAndLocalJurisdictionMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_StateAndLocalJurisdictionMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">State And Local Jurisdiction [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:type="locator" xlink:label="us-gaap_TaxCreditCarryforwardAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax Credit Carryforward</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxCreditCarryforwardAxis" xlink:to="us-gaap_TaxCreditCarryforwardAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Carryforward [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:type="locator" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax Credit Carryforward, Name</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxCreditCarryforwardNameDomain" xlink:to="us-gaap_TaxCreditCarryforwardNameDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Carryforward Name [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchMember" xlink:type="locator" xlink:label="us-gaap_ResearchMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Tax Credits</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchMember" xlink:to="us-gaap_ResearchMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ResearchMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Research [Member]</link:label>
    <link:label xml:lang="en-US" xlink:label="srt_MinimumMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Minimum</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxContingencyLineItems" xlink:type="locator" xlink:label="us-gaap_IncomeTaxContingencyLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxContingencyLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Contingency [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxContingencyLineItems" xlink:to="us-gaap_IncomeTaxContingencyLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeTaxContingencyLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Contingency [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:type="locator" xlink:label="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred tax asset, net change in total valuation allowance increase during period</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:to="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Allowance Deferred Tax Asset Change In Amount</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_OperatingLossCarryforwardsExpirationYear" xlink:type="locator" xlink:label="ctmx_OperatingLossCarryforwardsExpirationYear" />
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating loss carryforwards expiration year.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_OperatingLossCarryforwardsExpirationYear" xlink:to="ctmx_OperatingLossCarryforwardsExpirationYear_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed" xlink:type="locator" xlink:label="ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed" />
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating loss carryforwards amount to expire if not used.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed" xlink:to="ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed_lbl" />
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration" xlink:type="locator" xlink:label="ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration" />
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating loss carryforwards amount not subject to expiration.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration" xlink:to="ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLossCarryforwards" xlink:type="locator" xlink:label="us-gaap_OperatingLossCarryforwards" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLossCarryforwards_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net operating loss carryforwards</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLossCarryforwards" xlink:to="us-gaap_OperatingLossCarryforwards_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OperatingLossCarryforwards_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating loss carryforwards expiration year</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards Expiration Year</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating loss carryforwards to expire if not utilized</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards Amount To Expire If Not Used</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating loss carryforwards not subject to expiration</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards Amount Not Subject To Expiration</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_TaxCreditCarryforwardExpirationYear" xlink:type="locator" xlink:label="ctmx_TaxCreditCarryforwardExpirationYear" />
    <link:label xml:lang="en-US" xlink:label="ctmx_TaxCreditCarryforwardExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Tax credit carryforward expiration year.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_TaxCreditCarryforwardExpirationYear" xlink:to="ctmx_TaxCreditCarryforwardExpirationYear_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:type="locator" xlink:label="us-gaap_TaxCreditCarryforwardAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reduction to tax credit carryforwards</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxCreditCarryforwardAmount" xlink:to="us-gaap_TaxCreditCarryforwardAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_TaxCreditCarryforwardAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Carryforward Amount</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_TaxCreditCarryforwardExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax credit carryforward, expiration</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_TaxCreditCarryforwardExpirationYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Carryforward Expiration Year</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_PercentageOfChangeInOwnership" xlink:type="locator" xlink:label="ctmx_PercentageOfChangeInOwnership" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfChangeInOwnership_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of change in ownership.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_PercentageOfChangeInOwnership" xlink:to="ctmx_PercentageOfChangeInOwnership_lbl" />
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfChangeInOwnership_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of change in ownership</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_PercentageOfChangeInOwnership_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Change In Ownership</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:type="locator" xlink:label="us-gaap_UnrecognizedTaxBenefits" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrecognized tax benefits</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefits" xlink:to="us-gaap_UnrecognizedTaxBenefits_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" xlink:type="locator" xlink:label="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrecognized tax benefits would affect company&apos;s effective tax rate</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" xlink:to="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits That Would Impact Effective Tax Rate</link:label>
    <link:loc xlink:href="ctmx-20191231.xsd#ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" xlink:type="locator" xlink:label="ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" />
    <link:label xml:lang="en-US" xlink:label="ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of increase decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" xlink:to="ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions_lbl" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward" xlink:type="locator" xlink:label="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward" xlink:to="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance at the beginning of the year</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" xlink:type="locator" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additions based on tax positions related to current year</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" xlink:to="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustment based on tax positions related to prior years</link:label>
    <link:label xml:lang="en-US" xlink:label="ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits Increase Decrease Resulting From Prior Period Tax Positions</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance at end of the year</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued" xlink:type="locator" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest and penalties accrued</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued" xlink:to="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OpenTaxYear" xlink:type="locator" xlink:label="us-gaap_OpenTaxYear" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OpenTaxYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Open tax year</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OpenTaxYear" xlink:to="us-gaap_OpenTaxYear_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_OpenTaxYear_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Open Tax Year</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount" xlink:type="locator" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Company contributions to defined contribution plan</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount" xlink:to="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Employer Discretionary Contribution Amount</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net income (loss)</link:label>
    <link:label xml:lang="en-US" xlink:label="us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net loss per share attributable to common stockholders, basic and diluted</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTable" xlink:type="locator" xlink:label="us-gaap_SubsequentEventTable" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Table]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_SubsequentEventTable_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTable_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:type="locator" xlink:label="us-gaap_SubsequentEventTypeAxis" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeAxis_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:type="locator" xlink:label="us-gaap_SubsequentEventTypeDomain" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event Type</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventTypeDomain_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventTypeDomain_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventMember" xlink:type="locator" xlink:label="us-gaap_SubsequentEventMember" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventMember" xlink:to="us-gaap_SubsequentEventMember_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:type="locator" xlink:label="us-gaap_SubsequentEventLineItems" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Line Items]</link:label>
    <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SubsequentEventLineItems_lbl" />
    <link:label xml:lang="en-US" xlink:label="us-gaap_SubsequentEventLineItems_lbl" xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Line Items]</link:label>
  </link:labelLink>
</link:linkbase>
