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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-02-27T17:11:18.9699153+00:00 -->
<!-- Version            : 5.0.1.321 -->
<!-- Package ID         : b6652a6e5569493b992345213d961e9a -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="ctmx_ImmunoGenIncMember" name="ImmunoGenIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_NumberOfBusinessActivities" name="NumberOfBusinessActivities" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_SummaryOfSignificantAccountingPoliciesLineItems" name="SummaryOfSignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_SummaryOfSignificantAccountingPoliciesTable" name="SummaryOfSignificantAccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ProbodyTechnologyMember" name="ProbodyTechnologyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ComputerEquipmentAndSoftwareMember" name="ComputerEquipmentAndSoftwareMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_MoneyMarketFundsIncludedInRestrictedCashMember" name="MoneyMarketFundsIncludedInRestrictedCashMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ComputerEquipmentAndSoftwareGross" name="ComputerEquipmentAndSoftwareGross" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_GoodwillAbstract" name="GoodwillAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_GoodwillAndIntangibleAssetsLineItems" name="GoodwillAndIntangibleAssetsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ScheduleOfGoodwillAndIntangibleAssetsTable" name="ScheduleOfGoodwillAndIntangibleAssetsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AccruedResearchAndClinicalCurrent" name="AccruedResearchAndClinicalCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_AmgenIncMember" name="AmgenIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_PfizerIncMember" name="PfizerIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_NumberOfCollaborationAgreements" name="NumberOfCollaborationAgreements" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts" name="PercentageOfNetIncomeOrNetLossesRelatedToDevelopmentCosts" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_CD71AgreementMember" name="CD71AgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_SeattleGeneticsAgreementMember" name="SeattleGeneticsAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_DiscoveryAgreementMember" name="DiscoveryAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_DevelopmentRegulatoryAndCommercialMilestonePaymentsMember" name="DevelopmentRegulatoryAndCommercialMilestonePaymentsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_SecondTargetMember" name="SecondTargetMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_LicenseAgreementMember" name="LicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_RegentsOfTheUniversityOfCaliforniaMember" name="RegentsOfTheUniversityOfCaliforniaMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_UniversityOfCaliforniaSantaBarbaraMember" name="UniversityOfCaliforniaSantaBarbaraMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" name="ContingentPaymentsReceivableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_ContingentPaymentsReceivableProfitSplitOnSales" name="ContingentPaymentsReceivableProfitSplitOnSales" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod" name="MilestonePaymentsReceivedFromRevenueRecognizedDuringPeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_PaymentsOfSublicenseFees" name="PaymentsOfSublicenseFees" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_NumberOfTargets" name="NumberOfTargets" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_NumberOfTargetsSelected" name="NumberOfTargetsSelected" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ContingentMilestonePaymentsReceivable" name="ContingentMilestonePaymentsReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_MilestonePaymentReceived" name="MilestonePaymentReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_AggregateCollaborationTransactionAmount" name="AggregateCollaborationTransactionAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_EstimatedSublicenseFees" name="EstimatedSublicenseFees" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_NumberOfAccountingUnits" name="NumberOfAccountingUnits" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_MilestonePaymentsReceivable" name="MilestonePaymentsReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_RevenueAdjustmentOfMilestonePaymentRecognized" name="RevenueAdjustmentOfMilestonePaymentRecognized" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds" name="LicensePaymentPercentageEquivalenceToUpfrontAndMilestoneProceeds" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_EstimatedResearchServicePeriod" name="EstimatedResearchServicePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_CommonStockSharesIssuableUnderAgreement" name="CommonStockSharesIssuableUnderAgreement" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_PeriodUsedToCalculateWeightedAveragePricePerShare" name="PeriodUsedToCalculateWeightedAveragePricePerShare" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement" name="LockUpPeriodForShareTransactionUnderCollaborationAndLicenseAgreement" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_EstimatedPremiumOnIssuanceOfShares" name="EstimatedPremiumOnIssuanceOfShares" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_CollaborationAndLicenseAgreementMember" name="CollaborationAndLicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_EGFRProductsMember" name="EGFRProductsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_SublicenseAgreementMember" name="SublicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AmgenOtherProductsMember" name="AmgenOtherProductsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ProfitShareUponExerciseOfCoDevelopmentOption" name="ProfitShareUponExerciseOfCoDevelopmentOption" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_NumberOfAdditionalCollaborationTarget" name="NumberOfAdditionalCollaborationTarget" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" name="ContingentPaymentsPayableUponAchievingDevelopmentRegulatoryAndCommercialMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_PremiumOnIssuanceOfSharesAllocatedToCommonStock" name="PremiumOnIssuanceOfSharesAllocatedToCommonStock" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_EstimatedFairValueOfProducts" name="EstimatedFairValueOfProducts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_EstimatedFullTimeEmployeeHoursAndResearchServicePeriod" name="EstimatedFullTimeEmployeeHoursAndResearchServicePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_NumberOfOncologyTarget" name="NumberOfOncologyTarget" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_NumberOfCollaborationTarget" name="NumberOfCollaborationTarget" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_CollaborationTargetResearchTerm" name="CollaborationTargetResearchTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_PeriodOfNominationOfAdditionalTarget" name="PeriodOfNominationOfAdditionalTarget" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ExtensionOfResearchTermForEachCollaborationTarget" name="ExtensionOfResearchTermForEachCollaborationTarget" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_IncrementsOfExtendedCollaborationTargetResearchTimes" name="IncrementsOfExtendedCollaborationTargetResearchTimes" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_AchievingAdditionalTargetsMember" name="AchievingAdditionalTargetsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember" name="AchievementOfDevelopmentMilestonesForEachResearchTargetProgramMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" name="AchievementOfDevelopmentMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingFirstCommercialSaleInVariousTerritoriesMember" name="AchievingFirstCommercialSaleInVariousTerritoriesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember" name="AchievingFirstCommercialSaleIfFourResearchTargetsSelectedByCounterpartyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingSalesMilestonesForEachResearchTargetProgramMember" name="AchievingSalesMilestonesForEachResearchTargetProgramMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" name="AchievingSalesMilestonesIfFourResearchTargetsSelectedByCounterpartyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_PreClinicalCandidateMember" name="PreClinicalCandidateMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_DrugApplicationForCTLA4Member" name="DrugApplicationForCTLA4Member" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember" name="AchievementOfDevelopmentMilestonesIfEightResearchTargetsSelectedByCounterpartyMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingEightTargetsSelectedForFirstProductModalityMember" name="AchievingEightTargetsSelectedForFirstProductModalityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember" name="AchievingSalesMilestonesIfEightResearchTargetsSelectedForFirstProductModalityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingDevelopmentMilestonePaymentsMember" name="AchievingDevelopmentMilestonePaymentsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember" name="AchievingDevelopmentMilestonePaymentIfEightResearchTargetsAreSelectedForSecondProductModalityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember" name="AchievingMilestonePaymentsForFirstCommercialSaleInVariousTerritoriesForUpToThreeIndicationsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" name="AchievingMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingSalesMilestonePaymentsPerTargetMember" name="AchievingSalesMilestonePaymentsPerTargetMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" name="AchievingSalesMilestonePaymentIfEightResearchTargetAreSelectedForSecondProductModalityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ThirdAndFourthTargetsMember" name="ThirdAndFourthTargetsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_NumberOfResearchTargetsSelected" name="NumberOfResearchTargetsSelected" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_NumberOfSalesIndicatorsForEachResearchTargetProgram" name="NumberOfSalesIndicatorsForEachResearchTargetProgram" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_NumberOfNonOncologyTarget" name="NumberOfNonOncologyTarget" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ResearchAndDevelopmentServiceFees" name="ResearchAndDevelopmentServiceFees" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_EstimatedResearchServiceTerminationDate" name="EstimatedResearchServiceTerminationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_CashPaymentToExecuteAgreement" name="CashPaymentToExecuteAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_LicenseReceivablesMember" name="LicenseReceivablesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember" name="ResearchServicesJointResearchCommitteeParticipationAndTechnologyImprovementsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_MilestonesPaymentsMadeDuringPeriod" name="MilestonesPaymentsMadeDuringPeriod" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones" name="ContingentPaymentsReceivableUponAchievingDevelopmentAndRegulatoryMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_ContingentPaymentsReceivableUponAchievingSalesMilestones" name="ContingentPaymentsReceivableUponAchievingSalesMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones" name="ContingentPaymentsPayableUponAchievingDevelopmentAndRegulatoryMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_ContingentPaymentsPayableUponAchievingSalesMilestones" name="ContingentPaymentsPayableUponAchievingSalesMilestones" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_MilestonePaymentPayable" name="MilestonePaymentPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_EstimatedFairValueOfAssetsAndServices" name="EstimatedFairValueOfAssetsAndServices" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_OptionsExpirationDate" name="OptionsExpirationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_MDAndersonMember" name="MDAndersonMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_NumberOfNominatedResearchTargets" name="NumberOfNominatedResearchTargets" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_NumberOfAdditionalResearchTargetsWithNominationOption" name="NumberOfAdditionalResearchTargetsWithNominationOption" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ContractWithCustomerLiabilityAdditions" name="ContractWithCustomerLiabilityAdditions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_AmortizationPeriodOfDeferredRevenue" name="AmortizationPeriodOfDeferredRevenue" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_FirstTargetMember" name="FirstTargetMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ContractWithCustomerLiabilityMaturityMonthAndYear" name="ContractWithCustomerLiabilityMaturityMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_RoyaltyObligationsFutureMinimumPaymentsDue" name="RoyaltyObligationsFutureMinimumPaymentsDue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_LicenseTerminationPeriod" name="LicenseTerminationPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_SublicenseAndMaintenanceFeesMember" name="SublicenseAndMaintenanceFeesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_AbbVieMember" name="AbbVieMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_PaymentOfUpfrontFees" name="PaymentOfUpfrontFees" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_AnnualLicenseMaintenanceFees" name="AnnualLicenseMaintenanceFees" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_LicensePaymentTerm" name="LicensePaymentTerm" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_PercentageOfRemainingMaintenanceFeesOutstanding" name="PercentageOfRemainingMaintenanceFeesOutstanding" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_FairValueOfCommonStockIssued" name="FairValueOfCommonStockIssued" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_AdditionalSublicenseFees" name="AdditionalSublicenseFees" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_MilestonePaymentReceivable" name="MilestonePaymentReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_SublicenseFees" name="SublicenseFees" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_UpfrontLicensePayment" name="UpfrontLicensePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_FirstYearOfLeaseTermMember" name="FirstYearOfLeaseTermMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_SecondTwelveMonthsOfLeaseTermMember" name="SecondTwelveMonthsOfLeaseTermMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_TenthYearOfLeaseTermMember" name="TenthYearOfLeaseTermMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_OperatingLeasesRentExpenseAnnualBaseRent" name="OperatingLeasesRentExpenseAnnualBaseRent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_MaximumImprovementAllowance" name="MaximumImprovementAllowance" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_ImprovementAllowanceFromRecoverableRent" name="ImprovementAllowanceFromRecoverableRent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract" name="CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_SupplementalBalanceSheetInformationRelatedToLeasesAbstract" name="SupplementalBalanceSheetInformationRelatedToLeasesAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_WeightedAverageRemainingLeaseTermAbstract" name="WeightedAverageRemainingLeaseTermAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_WeightedAverageDiscountRateAbstract" name="WeightedAverageDiscountRateAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_UnderwrittenPublicOfferingMember" name="UnderwrittenPublicOfferingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_StockOptionsIssuedAndOutstanding" name="StockOptionsIssuedAndOutstanding" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForFutureIssuanceUnderEmployeeStockPurchasePlan" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRightsOfCommonStockHoldingPercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_TwoThousandFifteenStockIncentivePlanMember" name="TwoThousandFifteenStockIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_TwoThousandNineteenStockIncentivePlanMember" name="TwoThousandNineteenStockIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_EarlyExerciseOfEmployeeOptionsMember" name="EarlyExerciseOfEmployeeOptionsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_NonEmployeesMember" name="NonEmployeesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAuthorized" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantGrantsInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantExercisesInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeituresInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAuthorized" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice" name="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsAuthorizedWeightedAverageExercisePrice" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ctmx_EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation" name="EffectiveIncomeTaxRateReconciliationOperatingLossCarryForwardLimitation" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments" name="EffectiveIncomeTaxRateReconciliationReturnToProvisionAdjustments" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_DeferredTaxAssetsLeaseLiability" name="DeferredTaxAssetsLeaseLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_DeferredTaxLiabilitiesRightOfUseAssets" name="DeferredTaxLiabilitiesRightOfUseAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ctmx_OperatingLossCarryforwardsExpirationYear" name="OperatingLossCarryforwardsExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_OperatingLossCarryforwardsAmountToExpireIfNotUsed" name="OperatingLossCarryforwardsAmountToExpireIfNotUsed" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_OperatingLossCarryforwardsAmountNotSubjectToExpiration" name="OperatingLossCarryforwardsAmountNotSubjectToExpiration" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ctmx_TaxCreditCarryforwardExpirationYear" name="TaxCreditCarryforwardExpirationYear" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_PercentageOfChangeInOwnership" name="PercentageOfChangeInOwnership" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ctmx_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" name="UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
</xsd:schema>
