4,990

Accrued liabilities

21,416

16,382

Total current liabilities

52,997

40,559

86,274

61,147

Other long-term liabilities

236,365

264,704

2,426

1,897

Total liabilities

325,065

327,748

Commitments and contingencies

Stockholders' equity:

Common stock, $0.00001 par value; 75,000,000 shares authorized; 44,997,279 and 38,478,560 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively

Additional paid-in capital

440,616

289,454

Accumulated other comprehensive loss

(208)

(94)

Total stockholders' equity

(282,748)

(219,465)

157,661

69,896

Total liabilities and stockholders' equity

482,726

397,644

Convertible Preferred Stock

Stockholders' equity:

Convertible preferred stock, $0.00001 par value; 10,000,000 shares authorized and no shares issued and outstanding at September 30, 2018 and December 31, 2017.

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	44,997,279	38,478,560
Common stock, shares outstanding	44,997,279	38,478,560
Convertible Preferred Stock
Convertible Preferred stock, par value	$ 0.00001	$ 0.00001
Convertible Preferred stock, shares authorized	10,000,000	10,000,000
Convertible Preferred stock, shares issued	0	0
Convertible Preferred stock, shares outstanding	0	0

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue from related party		$ 482		$ 1,429
Total revenue	$ 12,509	24,144	$ 48,031	44,550
Operating expenses:
Research and development	27,549	28,920	75,560	71,573
General and administrative	8,137	6,249	24,535	17,989
Total operating expenses	35,686	35,169	100,095	89,562
Loss from operations	(23,177)	(11,025)	(52,064)	(45,012)
Interest income	2,219	806	5,134	1,400
Other income (expense), net	29	(47)	(50)	(101)
Loss before provision for income taxes	(20,929)	(10,266)	(46,980)	(43,713)
Provision for (benefit from) income taxes	2,502	(19)	5,391	7
Net loss	$ (23,431)	$ (10,247)	$ (52,371)	$ (43,720)
Net loss per share, basic and diluted	$ (0.53)	$ (0.28)	$ (1.29)	$ (1.19)
Shares used to compute net loss per share, basic and diluted	43,917,510	36,947,129	40,528,105	36,757,119
Other comprehensive income (loss):
Changes in unrealized gains (losses) on short-term investments	$ (30)	$ 49	$ (114)	$ (34)
Comprehensive loss	(23,461)	(10,198)	(52,485)	(43,754)
License and Service
Revenue	$ 12,509	$ 23,662	$ 48,031	$ 43,121

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (52,371)	$ (43,720)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Gain on disposal of property and equipment		(1)
Amortization of intangible assets	109
Depreciation and amortization	1,276	1,241
Amortization of premiums (accretion of discounts) on investments	(1,114)	392
Stock-based compensation expense	12,262	8,537
Non-cash acquisition of in-process research and development asset charged to expense		10,700
Deferred income taxes		7
Changes in operating assets and liabilities
Accounts receivable	10,083	1,976
Related party accounts receivable		86
Prepaid expenses and other current assets	(3,538)	(952)
Other assets	(20)	(98)
Accounts payable	2,795	(3,495)
Accrued liabilities, income tax payable and other long-term liabilities	10,552	4,124
Deferred revenue	(26,813)	169,574
Net cash (used in) provided by operating activities	(46,779)	148,371
Cash flows from investing activities:
Purchases of property and equipment	(2,669)	(1,325)
Purchases of short-term investments	(161,743)	(54,183)
Maturities of short-term investments	154,496	84,000
Net cash (used in) provided by investing activities	(9,916)	28,492
Cash flows from financing activities:
Proceeds from common stock issuance, net of underwriting discounts and issuance costs of $9,154	134,596
Proceeds from exercise of stock options and employee stock purchases	4,304	2,717
Net cash provided by financing activities	138,900	2,717
Net increase in cash, cash equivalents and restricted cash	82,205	179,580
Cash, cash equivalents and restricted cash, beginning of period	178,465	105,562
Cash, cash equivalents and restricted cash, end of period	260,670	285,142
Supplemental disclosures of noncash investing and financing items:
Purchases of property and equipment in accounts payable and accrued liabilities	233	79
Non-cash acquisition of in-process research and development asset charged to expense		$ 10,700
ASC 606
Supplemental disclosures of noncash investing and financing items:
Non-cash adjustment to deferred revenue resulting from the adoption of ASC 606	$ 10,912

Description of the Business	9 Months Ended
Description of the Business	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of the Business	1. Description of the Business CytomX Therapeutics, Inc. (the “Company”) is a clinical-stage, oncology-focused biopharmaceutical company with a vision of transforming lives with safer, more effective therapeutics. The Company is pioneering a novel class of investigational antibody therapeutics, based on its Probody™ therapeutic technology platform, for the treatment of cancer. The Probody therapeutic approach is designed to more specifically target antibody therapeutics to the tumor microenvironment and reduce drug activity in healthy tissue and in circulation. The Company is located in South San Francisco, California and was incorporated in the state of Delaware in September 2010. Stock Offering In July 2018, the Company completed an underwritten public offering of 5,867,347 shares of common stock at a price of $24.50 per share, which included 765,306 shares issued pursuant to the underwriters’ exercise of their option to purchase additional shares of common stock. The aggregate net proceeds received by the Company from the offering were approximately $134.6 million after deducting underwriting discounts and commissions and offering expenses of $9.2 million.

Basis of Presentation and Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

2. Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation

The accompanying interim condensed financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting.

Unaudited Interim Financial Information

The accompanying interim condensed financial statements and related disclosures are unaudited, have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for a fair statement of the results of operations for the periods presented.

The condensed balance sheet data as of December 31, 2017 was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. The condensed results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results to be expected for the full year or for any other future year or interim period. The accompanying condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC.

Use of Estimates

The preparation of the financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that sum to the total of the amounts shown in the condensed statements of cash flows (in thousands).

	As of September 30, 2018		As of December 31, 2017
Cash and cash equivalents	$	259,753	$	177,548
Restricted cash - non-current assets		917		917
Total	$	260,670	$	178,465

Restricted cash represents a standby letter of credit issued pursuant to an office lease entered in December 2015.

Contract Balances

Customer payments are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional.

Comprehensive Income (Loss)

The Company’s unrealized gains and losses on short-term investments represent the only component of other comprehensive income (loss) that is excluded from the reported net loss.

Revenue Recognition

The Company adopted ASC Topic 606 effective January 1, 2018 on a modified retrospective basis. As such, the prior period amounts were not restated and continue to be presented in accordance with ASC Topic 605. For the Company’s accounting policy on revenue recognition prior to January 1, 2018, refer to the 2017 Form 10-K filed with the SEC on March 7, 2018. The policy disclosed in this Quarterly Report on Form 10-Q is the Company’s policy under ASC Topic 606, which has been applied since January 1, 2018.

The Company’s revenues are primarily derived through its license, research, development and commercialization agreements. The terms of these types of agreements may include (i) licenses for the Company’s technology or programs, (ii) research and development services, and (iii) services or obligations in connection with participation in research or steering committees. Payments to the Company under these arrangements typically include one or more of the following: nonrefundable upfront and license fees, research funding, milestone and other contingent payments to the Company for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products.

The Company recognizes revenue when the customer obtains control of the promised goods or services, in an amount that reflects the consideration which the Company has received or expects to receive in exchange for those goods or services.

The Company assesses whether the promises in its arrangements with customers are considered distinct performance obligations that should be accounted for separately. Judgment is required to determine whether the license to the Company’s intellectual property is distinct from the research and development services or participation on steering committees.

The transaction price in each arrangement is allocated to the identified performance obligations based on the standalone selling price (“SSP”) of each distinct performance obligation, which requires judgment. In instances where SSP is not directly observable, such as when a license or service is not sold separately, SSP is determined using information that may include market conditions and other observable inputs. Due to the early stage of the Company’s licensed technology, the license of such technology is typically combined with research and development services and steering committee participation as one performance obligation. In these cases, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

The Company’s collaboration and license agreements may include contingent payments related to specified research, development and regulatory milestones. Such payments are typically payable under the collaborations when the collaboration partner claims or selects a target, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, or upon receipt of actual marketing approvals of a covered product or for additional indications. At each reporting date, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price by using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. Once determined, the transaction price is allocated to each performance obligation on a relative SSP basis. At the end of each subsequent reporting period, the Company re-evaluates the probability or achievement of each such milestone and any related constraint, and if necessary, adjusts its estimate of the overall transaction price.

The Company’s collaboration and license agreements may also include contingent payments related to sales-based milestones. Sales-based milestones are typically payable when annual sales of a covered product reach specified levels. Sales-based milestones are recognized at the later of when the associated performance obligation has been satisfied or when the sales occur. Unlike other contingency payments, such as regulatory milestones, sales-based milestones are not included in the transaction price based on estimates at the inception of the contract, but rather, are included when the sales or usage occur.

AbbVie Ireland Unlimited Company (“AbbVie”), one of the Company’s collaboration partners, entered into a license agreement with Seattle Genetics, Inc. (“SGEN”) to license certain intellectual property rights. As part of the Company’s collaboration agreement with AbbVie, the Company pays SGEN sublicense fees. These sublicense fees are treated as reductions to the transaction price and combined with the performance obligation to which they relate. Milestone payments, when considered probable of being reached and when a significant revenue reversal would not be probable of occurring, are also recorded net of the associated sublicense fees and included in the transaction price.

Adopted Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 replaced most existing revenue recognition guidance in U.S. GAAP. The standard permits the use of either the retrospective or cumulative effect transition method. Additionally, in March 2016, the FASB issued ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which clarifies the implementation guidance on principal versus agent considerations in ASU No. 2014-09. In April 2016, the FASB issued ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients, which relates to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. These standards (collectively Accounting Standard Codification Topic 606 (“ASC 606”) have the same effective date and transition date of January 1, 2018. The Company adopted ASC 606 on January 1, 2018, using the cumulative effect transition method. The Company elected to use the practical expedient for contract modifications whereby the aggregate effect of all modifications that occurred prior to the transition date can be reflected when identifying performance obligations and determining and allocating the transaction price.

The Company evaluated its contracts with customers under ASC 606. The impact of adopting ASC 606 on the Company’s results of operations, financial condition, and cash flows varies depending on the contract. The Company recorded adjustments upon the adoption of ASC 606 as a result of the different accounting treatment of its revenue agreements with respect to the inclusion of milestone payments in the initial transaction price and the method to be used to recognize upfront fees. Under the prior revenue recognition standard, milestone payments were recognized when earned and upfront fees were generally recognized as revenue over the research term on a straight-line basis if another method of revenue recognition did not more clearly match the pattern of delivery of goods or services to the customer. Under ASC 606, milestone payments are included in the initial transaction price when it is probable that a significant reversal of the milestone payment will not occur. In addition, the Company can no longer default to the straight-line method as the default method in recognizing revenue for goods or services delivered over time. As such, the amount and timing of revenue recognition for its collaboration agreements changed under ASC 606. The impact of the adoption of ASC 606 was an increase in the balance of deferred revenue and an increase in the accumulated deficit balance of $10.9 million on January 1, 2018 in the Company’s condensed Balance Sheet.

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed balance sheet line items (in thousands):

	As of September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Liabilities
Income tax payable	$	4,082			908		$	4,990
Deferred revenue - current		46,230			6,767			52,997
Deferred revenue - long-term		223,781			12,584			236,365
Stockholders' Equity
Accumulated deficit		(262,489	)		(20,259	)		(282,748	)

The following tables summarize the impact of adopting ASC 606 on select unaudited condensed statement of operations line items (in thousands, except per share data):

	Three Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Revenue	$	10,895		$	1,614		$	12,509
Loss from operations		(24,791	)		1,614			(23,177	)
Loss before provision for income taxes		(22,543	)		1,614			(20,929	)
Provision for income taxes		2,650			(148	)		2,502
Net loss		(25,193	)		1,762			(23,431	)
Net loss per share, basic and diluted		(0.57	)		0.04			(0.53	)

	Nine Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Revenue	$	55,944		$	(7,913	)	$	48,031
Loss from operations		(44,151	)		(7,913	)		(52,064	)
Loss before provision for income taxes		(39,067	)		(7,913	)		(46,980	)
Provision for income taxes		4,483			908			5,391
Net loss		(43,550	)		(8,821	)		(52,371	)
Net loss per share, basic and diluted		(1.07	)		(0.22	)		(1.29	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of cash flows line items (in thousands):

	Nine Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Cash flows from operating activities:
Net loss	$	(43,550	)	$	(8,821	)	$	(52,371	)
Changes in operating assets and liabilities:
Accrued liabilities, income tax payable and other long-term liabilities		9,644			908			10,552
Deferred revenue		(34,726	)		7,913			(26,813	)

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The new standard provides clarification on the cash flow presentation and classification of certain transactions, including debt prepayment or extinguishment, settlement of certain debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of certain insurance claims and distributions received from equity method investees. The Company adopted this standard in its first quarter ended March 31, 2018. The adoption of this standard had no impact on the Company’s financial statements for the three months and nine months ended September 30, 2018.

In November 2016, the FASB issued ASU No. 2016-18, Restricted Cash, Statement of Cash Flows (Topic 230). ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The Company adopted this standard in its first quarter ended March 31, 2018. The Company has revised the presentation of restricted cash in its Statements of Cash Flows and provided the additional disclosures required under this standard.

In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting. This accounting standard update provides clarity when a change to terms or conditions of a share-based payment award must be accounted for as a modification. The new guidance requires modification accounting if the vesting condition, fair value or the award classification is not the same both before and after a change to the terms and conditions of the award. The Company adopted this standard on January 1, 2018. The adoption of this standard had no impact on the Company’s financial statements for the three months and nine months ended September 30, 2018.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). Under ASU 2016-02, an entity will be required to recognize right-of-use assets and lease liabilities on its balance sheet and disclose key information about leasing arrangements. ASU 2016-02 offers specific accounting guidance for a lessee, a lessor and sale and leaseback transactions. Lessees and lessors are required to disclose qualitative and quantitative information about leasing arrangements to enable a user of the financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. For public companies, ASU 2016-02 is effective for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period, and required a modified retrospective adoption, with early adoption permitted. In July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases (“ASU 2018-10”) and ASU 2018-11, Targeted Improvements. ASU 2018-10 provides improvements and clarification to ASU 2016-02 in various areas, including implicit interest rates, lessee assessment of lease classification, lease term and purchase options and various other improvements. ASU 2018-11 provides another transition method by allowing entities to initially apply the new lease standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The Company plans to adopt Topic 842 beginning with its first quarter ending March 31, 2019. The Company is currently evaluating the impact of the lease standard on its financial statements. The Company anticipates that implementation of Topic 842 will result in an increase in assets and liabilities and additional disclosures. To date, the Company has created an inventory of its leases. The Company continues to evaluate the transition considerations, including the election of various practical expedients provided by the standard.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard changes the impairment model for most financial assets and certain other instruments. Under the new standard, entities holding financial assets and net investment in leases that are not accounted for at fair value through net income are to be presented at the net amount expected to be collected. An allowance for credit losses will be a valuation account that will be deducted from the amortized cost basis of the financial asset to present the net carrying value at the amount expected to be collected on the financial asset. The new standard will be effective for the Company on January 1, 2020. The Company is currently evaluating the impact of this new guidance.

In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The new standard simplifies the measurement of goodwill by eliminating the Step 2 impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. The new guidance requires an entity to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. Additionally, an entity should consider income tax effects from any tax-deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. The new guidance becomes effective for goodwill impairment tests in fiscal years beginning after December 15, 2019, though early adoption is permitted. The Company is currently evaluating the impact of this new guidance.

In February 2018, the FASB issued ASU No. 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this standard allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. The new standard will be effective for the Company on January 1, 2019. The Company is currently evaluating the impact of this new guidance.

In March 2018, the FASB issued ASU No. 2018-05, Income Taxes (Topic 740): Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 (SEC Update). This standard adds various SEC paragraphs pursuant to the issuance of SEC Staff Accounting Bulletin No. 118, which clarifies the SEC Staff’s views on income tax accounting implications of the Tax Cuts and Jobs Act (the “Tax Act”). It requires reporting of provisional amounts for specific income tax effects of the Tax Act for which the accounting under ASC Topic 740 will be incomplete, but a reasonable estimate can be determined. Provision amounts for income tax effects of the Tax Act for which a reasonable estimate cannot be determined, ASC Topic 740 should be applied based on provisions of the tax laws that were in effect immediately prior to the Tax Act being enacted. Provisional amounts for income tax effects for which a reasonable estimate cannot be determined would be reported in the first reporting period in which a reasonable estimate can be determined. The Company continues to analyze the impact of the Tax Act for which it can reasonably estimate in the three months and nine months ended September 30, 2018 (See Note 9, Income Tax Expense).

In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. The amendments in this ASU expand the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. This new guidance is effective for the Company on January 1, 2019 with early adoption permitted. The Company is currently evaluating the impact of this new guidance.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820). The amendments in this ASU modify the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurement. Various disclosure requirements have been removed, including the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for timing of transfers between levels, the valuation processes for Level 3 fair value measurements held at the end of the reporting period. The ASU also modified various disclosure requirements and added some disclosure requirements for Level 3 fair value measurements. The amendments in this ASU are effective for the Company on January 1, 2020. The additional disclosures on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. An entity is permitted to early adopt any removed or modified disclosures upon issuance of this ASU and delay adoption of the additional disclosures until their effective date. Currently, the Company does not expect the adoption of this ASU will have a material impact on its financial statements.

In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other- Internal-Use Software (Subtopic 350-40). The amendments in this ASU on the accounting for implementation, setup and other upfront costs (collectively “implementation costs”) apply to entities that are a customer in a hosting arrangement. The amendments under this ASU align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. Accordingly, the amendments in this ASU require an entity in a hosting arrangement that is a service contract to follow the guidance in Subtopic 350-40 to determine which implementation costs to expense. They also require an entity to expense the capitalized implementation costs of a hosting arrangement that is a service contract over the term of the hosting arrangement. This ASU is effective for the Company on January 1, 2020. The Company is currently evaluating the impact of this new guidance.

Fair Value Measurements and Short-Term Investments

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements and Short-Term Investments

3. Fair Value Measurements and Short-Term Investments

In accordance with ASC 820-10, Fair Value Measurements and Disclosures, the Company determines the fair value of financial and non-financial assets and liabilities using the fair value hierarchy, which establishes three levels of inputs that may be used to measure fair value, as follows:

•

Level I: Inputs which include quoted prices in active markets for identical assets and liabilities.

•

Level II: Inputs other than Level I that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

•

Level III: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

The carrying amounts of the Company’s financial instruments, including restricted cash, accounts receivable, accounts payable and accrued liabilities approximate their fair values due to their relatively short maturities. The Company’s financial instruments consist of Level I assets. Level I assets consist primarily of highly liquid money market funds, some of which are included in restricted cash, and U.S. government bonds that are included in short-term investments.

The following tables set forth the fair value of the Company’s short-term investments subject to fair value measurements on a recurring basis and the level of inputs used in such measurements (in thousands):

		September 30, 2018
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	130,543	$	—	$	—		$	130,543
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. government bonds	Level I		204,990		—		(181	)		204,809
Total		$	336,450	$	—	$	(181	)	$	336,269

		December 31, 2017
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	164,440	$	—	$	—		$	164,440
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. government bonds	Level I		196,629		—		(67	)		196,562
Total		$	361,986	$	—	$	(67	)	$	361,919

As of September 30, 2018, no securities have contractual maturities of longer than one year.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accrued Liabilities

9 Months Ended

Sep. 30, 2018

Accrued Liabilities Current [Abstract]

Accrued Liabilities

4. Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	September 30,		December 31,
	2018		2017
Research and clinical expenses	$	14,846	$	10,068
Payroll and related expenses		4,823		4,526
Legal and professional expenses		1,328		1,523
Other accrued expenses		419		265
Total	$	21,416	$	16,382

Research and Collaboration Agreements

9 Months Ended

Sep. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Research and Collaboration Agreements

5. Research and Collaboration Agreements

AbbVie Ireland Unlimited Company

In April 2016, the Company and AbbVie entered into two agreements, a CD71 Co-Development and Licensing Agreement (the “CD71 Agreement”) and a Discovery Collaboration and Licensing Agreement (the “Discovery Agreement” and together with the CD71 Agreement the “AbbVie Agreements”). Under the terms of the CD71 Agreement, the Company and AbbVie will co-develop a Probody Drug Conjugates (“PDC”) against CD71, with the Company responsible for pre-clinical and early clinical development. AbbVie will be responsible for later development and commercialization, with global late-stage development costs shared between the two companies. The Company will assume 35% of the net profits or net losses related to later development unless it opts-out. If the Company opts-out from participation of co-development of the CD71 PDC, AbbVie will have sole right and responsibility for the further development, manufacturing and commercialization of such CD71 PDC.

Under the CD71 Agreement, the Company received an upfront payment of $20.0 million in April 2016, and is eligible to receive up to $470.0 million in development, regulatory and commercial milestone payments, a 35% profit split on U.S. sales, and royalties on ex-U.S. sales in the high teens to low twenties if the Company participates in the co-development of the CD71 Licensed Product subject to a reversion to a royalty on U.S. sales, and reduction in royalties on ex-U.S. sales, if the Company opts-out from the co-development of the CD71 PDC. The Company’s share of later stage co-development costs for each CD71 PDC are capped, provided that AbbVie may offset the Company’s co-development cost above the capped amounts from future payments such as milestone payments and royalties. In July 2017, the Company received a milestone payment of $14.0 million (net of payment of an associated sublicense fee of $1.0 million to SGEN under the Seattle Genetics Agreement) from AbbVie for achieving certain milestones required to be met to begin GLP toxicology studies under the CD71 Agreement. In May 2018, the United States Food and Drug Administration (“FDA”) cleared the IND application for CX-2029, the PDC targeting CD71. As a result, the Company achieved the IND success criteria under the CD71 Agreement and received a $21.0 million milestone payment (net of the payment of an associated sublicense fee of $4.0 million to SGEN). The Company commenced enrollment of our Phase 1/2 clinical trial and dosed the first patient in a clinical trial at the end of the second quarter of 2018.

Under the terms of the Discovery Agreement, AbbVie receives exclusive worldwide rights to develop and commercialize PDCs against up to two targets, one of which was selected in March 2017. The Company shall perform research services to discover the Probody therapeutics and create PDCs for the nominated collaboration targets. From that point, AbbVie shall have sole right and responsibility for development and commercialization of products comprising or containing such PDCs (“Discovery Licensed Products”).

Under the Discovery Agreement, the Company received an upfront payment of $10.0 million in April 2016 and may receive an additional payment upon the selection by AbbVie of the second target and the satisfaction of certain success criteria under the CD71 Agreement. AbbVie has not selected the second target, but the success criteria under the CD71 Agreement were met in September 2016. The Company is also eligible to receive up to $275.0 million in target nomination, development, regulatory and commercial milestone payments and royalties in the high single to low teens from commercial sales of any resulting PDCs.

The Company has determined that the CD71 and Discovery Agreements with AbbVie should be combined and evaluated as a single arrangement in determining revenue recognition, because both agreements were concurrently negotiated and executed.

The Company identified the following performance obligations at the inception of the AbbVie Agreements: (1) the research, development and commercialization license for CD71 Probody therapeutic, (2) the research services related to CD71 Probody therapeutic, (3) the obligation to participate in the CD71 Agreement joint research committee, (4) the research services related to the first discovery target (5) the research, development and commercialization license for the first discovery target, and (6) the obligation to participate in the Discovery Agreement joint research committee. The Company concluded that, at the inception of the agreement, AbbVie’s option for the second discovery target is not a material right and is therefore not a performance obligation.

The Company determined that the research, development and commercialization licenses for CD71 and discovery targets are not distinct from the Company’s respective research services and expertise. The Company considered factors such as novelty of the Probody therapeutic and PDC technology and lack of other parties’ expertise in this space, the Company’s rights to technology relating to a proprietary platform to enable the Probody therapeutic development and AbbVie’s contractual obligation to use the Company’s research services. The Company determined that the CD71 Agreement research, development and commercialization license, related research service and participation in the joint research committee were a combined performance obligation and were distinct from the Discovery Agreement research, development and commercialization license, related research service and participation in the joint research committee. Therefore, the Company concluded that there are two distinct performance obligations: CD71 Agreement performance obligation consisting of the CD71 Agreement research, development and commercialization license, related research service and participation in the joint research committee, and the Discovery Agreement performance obligation consisting of the Discovery Agreement research, development and commercialization license, related research service and participation in the joint research committee.

The total transaction price upon adoption of ASC 606 on January 1, 2018 of $39.8 million consists of $30.0 million in upfront payments, $14.0 million milestone payment received (net of the payment of an associated sublicense fee of $1.0 million to SGEN) less $4.2 million of estimated sublicense fees. The upfront payments under the AbbVie Agreements are allocated between the two performance obligations based on the estimated relative standalone selling prices. The $30.0 million of upfront payments is allocated $20.0 million to the CD71 Agreement, with the remaining $10.0 million allocated to the Discovery Agreement. The $14.0 million milestone payment received (net of the payment of an associated sublicense fee of $1.0 million to SGEN) and estimated sublicense fees are allocated to the CD71 Agreement performance obligation as they are directly related to the development of the CD71 Probody therapeutic. In May 2018, the Company earned a $21.0 million milestone payment (net of the payment of an associated sublicense fee of $4.0 million to SGEN). The $21.0 million milestone payment was included as part of the transaction price in May 2018 and a revenue adjustment of $9.9 million was recognized in the second quarter of 2018 reflecting the percentage completed to-date on the project related to this milestone. The Company determined that the remaining potential milestone payments are probable of significant revenue reversal as their achievement is highly dependent on factors outside the Company’s control. Therefore, these payments have been fully constrained and were not included in the transaction price as of September 30, 2018. Under the UCSB Agreement, the Company is obligated to make royalty payments to UCSB equal to 5% of certain sublicense revenue payments owed to or received by the Company. As of September 30, 2018 and December 31, 2017, the Company accrued sublicense fees of $1.0 million and $0.5 million, respectively, under the CD71 Agreement. The Company recognized the initial transaction price upon adoption of ASC 606 on January 1, 2018 of $29.8 million allocated to the CD71 Agreement performance obligation using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company uses actual full-time employee (“FTE”) hours incurred relative to total estimated FTE hours expected to be incurred for the combined performance obligation. Revenue is recognized based on actual FTE hours incurred as a percentage of total estimated FTE hours as the Company completes its performance obligation over the five-year service period. As the Discovery Agreement performance obligation represents an obligation to continuously make the Company’s Probody therapeutic technology platform available to AbbVie, the initial transaction price of $10.0 million allocated to this performance obligation is recognized over the common measure of progress for the entire performance obligation over the estimated research service period of five years.

The Company recognized revenue of $2.8 million and $15.4 million for the three months ended September 30, 2018 and 2017, respectively, and $16.3 million and $18.1 million for the nine months ended September 30, 2018 and 2017, respectively, related to the AbbVie Agreements. As of September 30, 2018 and December 31, 2017, deferred revenue related to the CD71 Agreement performance obligation was $25.4 million and $11.2 million, respectively, and deferred revenue related to the Discovery Agreement performance obligation was $5.2 million and $6.8 million, respectively. As of both September 30, 2018 and December 31, 2017, no amount was due from AbbVie under the CD71 and Discovery Agreements.

Amgen, Inc.

On September 29, 2017, the Company and Amgen, Inc. (“Amgen”) entered into a Collaboration and License Agreement (the “Amgen Agreement”). Pursuant to the Amgen Agreement, the Company received an upfront payment of $40.0 million in October 2017. Concurrent with the entry into the Amgen Agreement, the Company and Amgen entered into a Share Purchase Agreement (the “Purchase Agreement”) pursuant to which Amgen purchased 1,156,069 shares of the Company’s common stock, par value $0.00001 per share, at a price of $17.30 per share (calculated based on a 20-day volume-weighted average price), for total proceeds of $20.0 million, which the Company received on October 6, 2017, the closing date of the transaction. The Company estimated a premium on the stock sold to Amgen of $0.5 million, which takes into account a discount due to the lack of marketability resulting from the six-month lockup period.

Under the terms of the Amgen Agreement, the Company and Amgen will co-develop a Probody T-cell engaging bi-specific therapeutic targeting EGFR (“EGFR Products”). The Company is responsible for early-stage development of EGFR Products and all related costs (up to certain pre-set costs and certain limits based on clinical study size). Amgen will be responsible for late-stage development, commercialization, and all related costs of EGFR Products. Following early-stage development, the Company will have the right to elect to participate financially in the global co-development of EGFR Products with Amgen, during which the Company would bear certain of the worldwide development costs for EGFR Products and Amgen would bear the rest of such costs (the “EGFR Co-Development Option”). If the Company exercises its EGFR Co-Development Option, the Company will share in somewhat less than 50% of the profit and losses from sales of such EGFR Products in the U.S., subject to certain caps, offsets, and deferrals. If the Company chooses not to exercise its EGFR Co-Development Option, the Company will not bear any costs of later stage development. The Company is eligible to receive up to $455.0 million in development, regulatory, and commercial milestone payments for EGFR Products, and royalties in the low-double-digit to mid-teen percentage of worldwide commercial sales, provided that if the Company exercises its EGFR Co-Development option, it shall receive a profit and loss split of sales in the U.S. and royalties in the low-double-digit to mid-teen percentage of commercial sales outside of the U.S..

Amgen also has the right to select a total of up to three targets, including the two additional targets discussed below. The Company and Amgen collaborate in the research and development of Probody T-cell engaging bi-specifics products directed against such targets. Amgen has selected one such target (the “Amgen Other Product”). If Amgen exercises its option within a specified period of time, it can select two such additional targets (the “Amgen Option Products” and, together with the Amgen Other Product, the “Amgen Products”). Except with respect to preclinical activities to be conducted by CytomX, Amgen will be responsible, at its expense, for the development, manufacture, and commercialization of all Amgen Products. If Amgen exercises all of its options and advances all three of the Amgen Products, CytomX is eligible to receive up to $950.0 million in upfront, development, regulatory, and commercial milestones and tiered high single-digit to low-teen percentage royalties. The Company concluded that, at the inception of the agreement, Amgen’s option to select the two additional targets is not a material right and does not represent a performance obligation of the agreement.

At the initiation of the collaboration, CytomX had the option to select, from programs specified in the Amgen Agreement, an existing pre-clinical stage T-cell engaging bispecific product from the Amgen pre-clinical pipeline. In March 2018, CytomX selected the program. CytomX is responsible, at its expense, for converting this program to a Probody T-cell engaging bispecific product, and thereafter, will be responsible for development, manufacturing, and commercialization of the product (“CytomX Product”). Amgen is eligible to receive up to $203.0 million in development, regulatory, and commercial milestone payments for the CytomX Product, and tiered mid-single digit to low double-digit percentage royalties.

The Company considered the criteria for combining contracts in ASC 606 and determined that the Amgen Agreement and the Purchase Agreement should be combined into one contract. The Company accounted for the Amgen Agreement based on the fair values of the assets and services exchanged. The Company identified the following performance obligations at the inception of the Amgen Agreement: (1) the research, development and commercialization license, (2) the research and development services for the EGFR Products and the Amgen Other Product, and (3) the obligation to participate in the joint steering committee (“JSC”) and the joint research committee (“JRC”). The Company determined that research, development and commercialization license and the participation in the JSC and JRC are not distinct from the research and development services and therefore those performance obligations were combined into one combined performance obligation. The Amgen Other Products are accounted for as a separate performance obligation from the EGFR Products as the nature of the services being performed is not the same and the value that Amgen can derive from one program is not dependent on the success of the other.

Concurrent with the execution of the Amgen Agreement, the Company entered into a sublicense agreement whereby the Company granted Amgen a sublicense of its rights to one patent family that it co-owns with the Regents of the University of California, acting through its Santa Barbara campus (“UCSB”), that is exclusively licensed to the Company under the UCSB Agreement covering Probody antibodies and other pro-proteins in the fields of therapeutics, in vivo diagnostics and prophylactics. This sublicense was incremental to the patents, patent applications and know-how covering T-cell engaging bispecific Probody molecules that were developed and owned by the Company and licensed to Amgen. Under the UCSB Agreement, the Company is obligated to make a royalty payment to UCSB equal to 15% of certain sublicense revenue payments owed to or received by the Company. The Company determined that the calculation of the sublicense fee is not specifically addressed in the sublicense agreement when the Company simultaneously licenses the UCSB technology along with the technology the Company has developed internally. As of December 31, 2017, the Company recorded a liability of $2.1 million, which represents the Company’s best estimate of the amount to be remitted to UCSB. As of September 30, 2018, the Company determined that the estimated liability of $2.1 million was still appropriate.

The total transaction price of $51.2 million, consisting of the $40.0 million upfront payment, an estimated fair value of $10.7 million for the CytomX Product and $0.5 million of premium on the sale of the Company’s common stock, was allocated between two performance obligations based on the relative standalone selling price of each performance obligation. To determine the standalone selling price, the Company used the discounted cash flow method by calculating risk-adjusted net present values of estimated cash flows. The Company determined that the remaining potential milestone payments were probable of significant revenue reversal as their achievement was highly dependent on factors outside the Company’s control. As a result, these payments were fully constrained and were not included in the transaction price as of September 30, 2018. The Company recognizes the transaction price of $45.8 million allocated to the EGFR Products performance obligation using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company uses actual costs incurred relative to budgeted costs expected to be incurred for the combined performance obligation. These costs consist primarily of internal FTE effort and third-party contract costs. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation over the six-year service period. As the Amgen Other Product performance obligation represents an obligation to continuously make the Probody therapeutic technology platform available to Amgen, the initial transaction price of $4.7 million allocated to this performance obligation is recognized over the common measure of progress for the entire performance obligation over the estimated research service period of six years.

The Company recognized revenue of $1.5 million and $4.4 million for the three and nine months ended September 30, 2018, respectively, related to the Amgen Agreement. There were no amounts recognized during the three and nine months ended September 30, 2017. As of September 30, 2018 and December 31, 2017, deferred revenue related to the EGFR Products performance obligation was $41.0 million and $45.3 million, respectively. As of September 30, 2018 and December 31, 2017, deferred revenue related to the Amgen Other Products performance obligation was $4.0 million and $4.6 million, respectively. As of September 30, 2018, no amount was due from Amgen under the Amgen Agreement.

Bristol-Myers Squibb Company

On May 23, 2014, the Company and Bristol-Myers Squibb Company (“BMS”) entered into a Collaboration and License Agreement (the “BMS Agreement”) to discover and develop compounds for use in human therapeutics aimed at multiple immuno-oncology targets using the Company’s Probody therapeutic technology. The effective date of the BMS Agreement was July 7, 2014.

Under the terms of the BMS Agreement, the Company granted BMS exclusive worldwide rights to develop and commercialize Probody therapeutics for up to four oncology targets. BMS had additional rights to substitute up to two collaboration targets within three years of the effective date of the BMS Agreement. These rights expired in May 2017. Each collaboration target has a two-year research term and the two additional targets must be nominated by BMS within five years of the effective date of the BMS Agreement. The research term for each collaboration target can be extended in one year increments up to three times.

Pursuant to the BMS Agreement, the financial consideration from BMS was comprised of an upfront payment of $50.0 million and the Company was initially entitled to receive contingent payments of up to an aggregate of $1,217.0 million as follows: (i) up to $25.0 million for additional targets; (ii) up to $114.0 million in development milestone payments per research target program or up to $456.0 million if the maximum of four research targets are selected; (iii) up to $124.0 million in milestone payments for the first commercial sale in various territories for up to three indications per research target program or up to $496.0 million if the maximum of four research targets are selected, and (iv) up to $60.0 million in sales milestones payments per research target program or up to $240.0 million if maximum of four research targets are selected. The Company is entitled to royalty payments in the mid-single digits to low double-digit percentages from potential future sales. The Company also receives research and development service fees based on a prescribed FTE rate that is capped.

The Company identified the following performance obligations at the inception of the BMS Agreement: (1) the exclusive research, development and commercialization license, (2) the research and development services and (3) the obligation to participate in the joint research committee. The Company determined that the license, the Company’s research services and expertise related to the development of the product candidates should be combined with the research services and participation in the joint research committee as one combined performance obligation. The Company concluded that, at the inception of the agreement, BMS’ options for the third and fourth targets were not material rights and not performance obligations. As such, each option was accounted for as a separate arrangement upon exercise. Additionally, the Company considered whether the services performed for each target should be considered separate performance obligations and concluded that all targets should be accounted for as one combined performance obligation.

The Company received an upfront payment of $50.0 million from BMS in July 2014. In January and December 2016, BMS selected the third and fourth targets, respectively, and paid the Company $10.0 million and $15.0 million, respectively, pursuant to the terms of the BMS Agreement. In December 2016, BMS selected a clinical candidate pursuant to the BMS Agreement, which triggered a $2.0 million pre-clinical milestone payment to the Company. In November 2017, the Company recognized a $10.0 million milestone payment from BMS upon approval of the investigational new drug application for the CTLA-4-directed Probody therapeutic.

On March 17, 2017, the Company and BMS entered into Amendment Number 1 to Extend Collaboration and License Agreement (the “Amendment”). The Amendment grants BMS exclusive worldwide rights to develop and commercialize Probody therapeutics for up to six additional oncology targets and two non-oncology targets. The effective date of the Amendment was April 25, 2017 (“Amendment Effective Date”).

Under the terms of the Amendment, the Company continues to collaborate with BMS to discover and conduct preclinical development of Probody therapeutics against targets selected by BMS under the terms of the Amendment.

Pursuant to the Amendment, the financial consideration from BMS is comprised of an upfront payment of $200.0 million and the Company is eligible to receive up to an aggregate of $3,586.0 million as follows: (i) up to $116.0 million in development milestone payments per target or up to $928.0 million if the maximum of eight targets are selected for the first product modality; (ii) up to $124.0 million in milestone payments for the first commercial sale in various territories for up to three indications per target program or up to $992.0 million if the maximum of eight targets are selected for the first product modality; (iii) up to $60.0 million in sales milestone payments per target or up to $480.0 million if maximum of eight targets are selected for the first product modality; and (iv) up to $56.3 million in development milestone payments or up to $450.0 million if the maximum of eight targets are selected for the second product modality; (v) up to $62.0 million in milestone payments for the first commercial sale in various territories for up to three indications per target program or up to $496.0 million if the maximum of eight targets are selected for the second product modality; (vi) up to $30.0 million in sales milestone payments per target or up to $240.0 million if maximum of eight targets are selected for the second product modality. The Company is also entitled to tiered mid-single to low double-digit percentage royalties from potential future sales. The Amendment does not change the term of the BMS’s royalty obligation under the BMS Agreement. BMS’s royalty obligation continues on a licensed-product by licensed-product basis until the later of (i) the expiration of the last claim of the licensed patents covering the licensed products in the country, (ii) the twelfth anniversary of the first commercial sale of a licensed product in a country, or (iii) the expiration of any applicable regulatory, pediatric, orphan drug or data exclusivity with respect to such product.

The initial transaction price is $272.8 million consisting of the upfront fees of $250.0 million, research and development service fees of $10.8 million and milestone payments received to date of $12.0 million. The Company determined that the remaining potential milestone payments were probable of significant revenue reversal as their achievement was highly dependent on factors outside the Company’s control. Therefore, these payments were fully constrained and were not included in the transaction price as of September 30, 2018. The BMS Agreement represents an obligation to continuously make the Probody therapeutic technology platform available to BMS. Therefore, the initial transaction price is recognized over the estimated research service period, which ends on April 25, 2023.

The Company recognized revenue of $8.2 million during each of the three months ended September 30, 2018 and 2017, respectively, and $24.6 million and $18.4 million for the nine months ended September 30, 2018 and 2017, respectively. As of September 30, 2018 and December 31, 2017, deferred revenue related to the BMS Agreement was $213.8 million and $235.0 million, respectively. The amount due from BMS under the BMS Agreement was $56,000 and $10.1 million as of September 30, 2018 and December 31, 2017, respectively.

ImmunoGen, Inc.

In January 2014, the Company and ImmunoGen, Inc. (“ImmunoGen”) entered into the Research Collaboration Agreement (the “ImmunoGen Research Agreement”). The ImmunoGen Research Agreement provided the Company with the right to use ImmunoGen’s Antibody Drug Conjugate (“ADC”) technology in combination with the Company’s Probody therapeutic technology to create a PDC directed at one specified target under a research license, and to subsequently obtain an exclusive, worldwide development and commercialization license to use ImmunoGen’s ADC technology to develop and commercialize such PDCs. The Company made no upfront cash payment in connection with the execution of the agreement. Instead, the Company provided ImmunoGen with the rights to CytomX’s Probody therapeutic technology to create PDCs directed at two targets under the ImmunoGen Research Agreement and to subsequently obtain exclusive, worldwide development and commercialization licenses to develop and commercialize such PDCs. In February 2016, the Company exercised its option to obtain a development and commercialization license for CX-2009 pursuant to the terms of the ImmunoGen Research Agreement (the “CX-2009 License”). In February 2017, ImmunoGen exercised its first option to obtain a development and commercialization license for one of the two targets. Substitution rights for this program terminated in February 2017 and ImmunoGen discontinued the program in July 2017. The Company recognized the remaining deferred revenue related to the discontinued program upon the termination of the program. ImmunoGen exercised its second option to obtain a development and commercialization license pursuant to the ImmunoGen Research Agreement (the “ImmunoGen 2017 License”) for a target in December 2017 and continues research work on this program.

Under the terms of the ImmunoGen Research Agreement, both the Company and ImmunoGen performed research activities on behalf of the other party for no monetary consideration through January 2018 and the arrangement was extended to June 2018, as discussed below. Each party is solely responsible for the development, manufacturing and commercialization of any products resulting from the exclusive development and commercialization license obtained by such party under the agreement.

In consideration for the ImmunoGen 2017 License, the Company is entitled to receive up to $30.0 million in development and regulatory milestone payments, up to $50.0 million in sales milestone payments and royalties in the mid-single digits on the commercial sales of any resulting product. For the CX-2009 License, the Company is obligated to pay ImmunoGen up to $60.0 million in development and regulatory milestone payments and up to $100.0 million in sales milestone payments and royalties in the mid to high single digits on the commercial sales of any resulting product. In August 2017, the Company made a milestone payment of $1.0 million to ImmunoGen for the first patient dosing with CX-2009. No milestone payments have been accrued to the Company under the ImmunoGen 2017 License.

The Company accounted for the ImmunoGen Research Agreement based on the fair value of the assets and services exchanged. The Company identified the following performance obligations at the inception of the ImmunoGen Research Agreement: (1) the research license, (2) the research services, (3) the obligation to participate in the joint research committee, (4) the exclusive research, development and commercialization license and (5) the obligation to provide future technology improvements, when available. The Company determined that the research license, participation in the joint steering committee, the research services, and the technology improvements are not distinct from the development and commercialization license and therefore those performance obligations were combined into one combined performance obligation. The Company considered factors such the limited economic benefits to ImmunoGen if the development and commercialization license was not obtained and the lack of sublicensing rights in the research license.

The estimated total fair value of the consideration of $13.2 million was recorded as deferred revenue at the inception of the ImmunoGen Research Agreement. In December 2017, the Company entered into the ImmunoGen 2017 License and extended the Company’s obligation to provide research services under the ImmunoGen Research Agreement to June 30, 2018. The fair value of the consideration for the combined performance obligation was recognized as revenue over the research period that ended on June 30, 2018. As of June 30, 2018, neither company has further research obligations under the ImmunoGen Research Agreement.

The estimated fair value of assets and services received was also $13.2 million, of which $12.7 million was allocated to the licenses received and was charged to research and development expense, with the remaining amount of $0.5 million allocated to the research services, joint research committee participation and technology improvements, which was expensed over the period of services provided.

The Company recognized revenue of $0 and $83,000 for the three months ended September 30, 2018 and 2017, respectively and $1.5 million and $6.6 million for the nine months ended September 30, 2018 and 2017, respectively. As of September 30, 2018 and December 31, 2017, deferred revenue relating to the ImmunoGen Research Agreement was $0 and $0.7 million, respectively. As of both September 30, 2018 and December 31, 2017, no amount was due from ImmunoGen under the ImmunoGen Research Agreement.

MD Anderson

In November 2015, the Company entered into a research collaboration agreement with MD Anderson to research Probody-enabled chimeric antigen receptor killer (CAR-NK) cell therapies, known as ProCAR-NK cell therapies. Under this collaboration, MD Anderson will use the Company’s Probody technology to conduct research of ProCAR-NK cell therapies against certain targets selected by the Company in cancer immunotherapy. Under the research collaboration agreement, the Company had the right to exercise an option, during the option period expiring on November 2, 2019 and upon payment of an option exercise fee, to negotiate and acquire a worldwide, exclusive, sublicensable license from MD Anderson for development and commercialization of products directed against any of the selected targets. The research collaboration agreement continued in effect until the earlier of (i) the date that the Company exercises the option to acquire the license from MD Anderson and (ii) the expiration of the option period. The expenses related to this agreement were not material to the financial statements for the three and nine months ended September 30, 2018 and 2017. The Company decided not to exercise the option to extend the agreement and allowed it to expire on November 1, 2018.

Pfizer Inc.

In May 2013, the Company and Pfizer Inc. (“Pfizer”) entered into a Research Collaboration, Option and License Agreement (the “Pfizer Agreement”) to collaborate on the discovery and preclinical research activities related to Probody therapeutics, and PDCs for research project targets nominated by Pfizer. Pfizer nominated two research targets in 2013 and, pursuant to the Pfizer Agreement, had the option of nominating two additional research targets. In December 2014, Pfizer selected an additional research target and paid the Company $1.5 million. The option to select a fourth target lapsed in May 2016. Pfizer discontinued the epidermal growth factor receptor (“EGFR”) program and decided to terminate the remaining two targets in February and March 2018. In March 2018, Pfizer terminated the Pfizer Agreement. As such, the Company had no further performance obligations under this agreement following the termination of the Pfizer Agreement and recognized the remaining deferred revenue of $1.1 million during the three months ended March 31, 2018.

Pursuant to the Pfizer Agreement, the Company received an upfront payment of $6.0 million and research and development service fees based on a prescribed FTE rate per year that is capped. The Company identified the following performance obligations at the inception of the Pfizer Agreement: (1) the research license, (2) the research services and (3) the obligation to participate in the joint research committee. The Company determined that the research license was not distinct from the research services and participation in the joint research committee due to the specialized nature of the research services to be provided by the Company, and accordingly, this deliverable was combined with the research services and participation in the joint research committee as a combined performance obligation. The Company concluded that, at the inception of the agreement, Pfizer’s options to obtain an exclusive development and commercialization license for each research project target did not represent a material right and were not performance obligations.

As the combined performance obligation represented an obligation to continuously make the Probody therapeutic technology platform available to Pfizer, the initial transaction price was recognized over the common measure of progress for the entire performance obligation over the estimated research service period of five and a half years.

The Company recognized revenue of $0 and $0.5 million for the three months ended September 30, 2018 and 2017, respectively, and $1.4 million both the nine months ended September 30, 2018 and 2017. As of September 30, 2018 and December 31, 2017, deferred revenue relating to the Pfizer Agreement was $0 and $1.6 million, respectively. The amount due from Pfizer under the Pfizer Agreement was $0 and $13,000 as of September 30, 2018 and December 31, 2017, respectively.

Contract Liabilities

The following table presents changes in the Company’s total contract assets and liabilities during the nine months ended September 30, 2018 (in thousands):

			Additions				Deductions
	Balance at 12/31/2017		ASC 606 Adoption Adjustment		Adjustment to Transaction Price from Performance Obligation Satisfied		Revenue Recognized from an Adjustment to Transaction Price During the Period			Revenue Recognized from Amounts Included in Contract Liability at the Beginning of the Period			Balance at 9/30/2018
Contract liabilities:
Deferred revenue	$	305,263	$	10,912	$	21,000	$	(10,799	)	$	(37,014	)	$	289,362

Additions of $31.9 million consists of the ASC 606 adoption adjustment of $10.9 million and $21.0 million earned (net of the payment of an associated sublicense fee of $4.0 million to SGEN) resulting from the achievement of the IND milestone under the CD71 Agreement. The $21.0 million milestone payment is included in the transaction price and is being recognized over the research period of the CD71 Agreement. Of the $21.0 million, $10.8 million was recognized as revenue during the nine months ended September 30, 2018 based on the estimated percentage completed to-date of the CD71 project. Deductions also includes $37.0 million of revenue recognized during the nine months ended September 30, 2018 that was included in the contract liability balance at the beginning of the period.

The Company estimates that the $289.4 million of deferred revenue related to the following contracts as of September 30, 2018 will be recognized as revenue as set forth below. However, the timing of revenue recognition could differ from the estimates depending on facts and circumstances impacting the various contracts, including progress of research and development, resources assigned to the contracts by the Company or its collaboration partners or other factors outside of the Company’s control.

•

The $25.4 million of deferred revenue related to the CD71 Agreement as of September 30, 2018 is expected to be recognized based on actual FTE effort and program progress until approximately April 2021.

•

The $5.2 million of deferred revenue related to the Discovery Agreement as of September 30, 2018 is expected to be recognized ratably until approximately April 2021.

•

The $41.0 million of deferred revenue related to the Amgen EGFR Products as of September 30, 2018 is expected to be recognized based on actual FTE effort and program progress until approximately September 2023.

•

The $4.0 million of deferred revenue related to the Amgen Other Products as of September 30, 2018 is expected to be recognized ratably until approximately September 2023.

•

The $213.8 million of deferred revenue related to the BMS Agreement as of September 30, 2018 is expected to be recognized ratably until approximately April 2025.

License Agreement	9 Months Ended
License Agreement	Sep. 30, 2018
Research And Development [Abstract]
License Agreement	6. License Agreement The Company has an exclusive, worldwide license agreement (the “UCSB Agreement”) with UCSB, relating to the use of certain patents and technology relating to its core technology, including its therapeutic antibodies, and to certain patent rights the Company co-owns with UCSB covering Probody antibodies and other pro-proteins. Pursuant to the UCSB Agreement, the Company is obligated to (i) make royalty payments to UCSB on net sales of its products covered under the agreement, subject to annual minimum amounts, (ii) make milestone payments to UCSB upon the occurrence of certain events, (iii) make a milestone payment to UCSB upon occurrence of an IPO or change of control, and (iv) reimburse UCSB for prosecution and maintenance of the licensed patents. If the Company sublicenses its rights under the UCSB Agreement, it is obligated to pay UCSB a percentage of the total sublicense revenue received, which total amount would be first reduced by the aggregate amount of certain research and development related expenses incurred by the Company and other permitted deductions. In 2013, the Company amended the UCSB Agreement to reduce certain amounts due to UCSB upon receipt by the Company of upfront payments, milestone payments and royalties from sublicenses. In exchange for this amendment, the Company issued to UCSB 157,332 shares of its common stock. The UCSB Agreement, as amended, remains in effect until the expiration or abandonment of the last to expire of the licensed patents. The Company incurred expenses of $0.1 million and $1.7 million for the three months ended September 30, 2018 and 2017, respectively, and $0.6 million and $12.0 million for the nine months ended September 30, 2018 and 2017, respectively, to UCSB under the provisions of the UCSB Agreement. Royalty obligations The Company has annual minimum royalty obligations of $150,000 under the terms of certain exclusive licensed patent rights. The royalty obligations are cancellable any time by giving notice to the licensor, with the termination being effective 60 days after giving notice.

Stock-Based Compensation

9 Months Ended

Sep. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

7. Stock-Based Compensation

Stock Options

Activities under the Company’s stock option plans for the nine months ended September 30, 2018 were as follows:

	Options Outstanding
	Number of Options			Weighted- Average Exercise Price Per Share
Balances at December 31, 2017		6,503,458		$	8.157
Options granted		1,921,900			25.760
Options exercised		(631,539	)		6.253
Option forfeited/expired		(111,764	)		17.248
Balances at September 30, 2018		7,682,055		$	12.586
Options exercisable at September 30, 2018		4,183,476		$	7.262

Stock-based Compensation

Total stock-based compensation recorded related to options granted to employees and non-employees and employee stock purchase plan was as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Stock-based compensation expense:
Research and development	$	2,131	$	1,267	$	5,989	$	3,813
General and administrative		2,282		1,514		6,273		4,724
Total stock-based compensation expense	$	4,413	$	2,781	$	12,262	$	8,537

Net Loss Per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Net Loss Per Share

8. Net Loss Per Share

The following weighted-average outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented, because including them would have been anti-dilutive:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Options to purchase common stock		7,292,701		6,713,038		7,434,862		6,976,470
Total		7,292,701		6,713,038		7,434,862		6,976,470

Income Tax Expense	9 Months Ended
Income Tax Expense	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Tax Expense	9. Income Tax Expense The Company recorded a provision for income taxes of $2.5 million and $5.4 million during the three and nine months ended September 30, 2018, respectively. The income tax expense was generated as a result of a timing difference in the recognition of revenue between tax and U.S. GAAP purposes, primarily related to the upfront payment received from the BMS Agreement and the Amgen Agreement in 2017. This timing difference will be recognized as revenue for tax purposes in 2018, which will generate taxable income and therefore, tax expense. The Company’s effective tax rate was (12.0)% and 0.2% for the three months ended September 30, 2018 and 2017, respectively, and (11.5)% and 0.0% for the nine months ended September 30, 2018 and 2017, respectively. Income tax expense for the three and nine months ended September 30, 2018 was accrued based on the newly-enacted statutory federal tax rate of 21%, which was effective for tax years starting on January 1, 2018. As of September 30, 2018, the Company maintained a full valuation allowance against its net deferred tax assets due to its history of losses. On December 22, 2017, the Tax Act of 2017 was signed into law making significant changes to the Internal Revenue Code. The Tax Act contains significant changes to corporate income tax, including among other things, a reduction to the corporate income tax rate from a top marginal rate of 35% to a flat rate of 21%. Since further guidance, interpretations and rulings are expected in the 12 months following enactment, the Company has made certain provisional estimates, as permitted by SAB 118 and continues to analyze the impact of the Tax Act. As of September 30, 2018, the Company had not completed its accounting for all of the effects of the Tax Act due to pending guidance, interpretations and rulings to be issued. The Company did not make any adjustments during the three and nine months ended September 30, 2018 to its tax amounts recorded during the year ended December 31, 2017. As the Company collects and prepares the necessary data and obtains further guidance or interpretation of the Tax Act, it may make adjustments to the provisional amounts that it has recorded that may materially impact the provision for income taxes in the period in which the adjustments are made. The Company will complete its accounting analysis when the interpretations, guidance and rulings are finalized by the various tax and standard-setting bodies, which is expected by the end of December 2018.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation

Unaudited Interim Financial Information

Use of Estimates

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

	As of September 30, 2018		As of December 31, 2017
Cash and cash equivalents	$	259,753	$	177,548
Restricted cash - non-current assets		917		917
Total	$	260,670	$	178,465

Restricted cash represents a standby letter of credit issued pursuant to an office lease entered in December 2015.

Contract Balances

Comprehensive Income (Loss)

The Company’s unrealized gains and losses on short-term investments represent the only component of other comprehensive income (loss) that is excluded from the reported net loss.

Revenue Recognition

Adopted Accounting Pronouncements and Recent Accounting Pronouncements

Adopted Accounting Pronouncements

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed balance sheet line items (in thousands):

	As of September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Liabilities
Income tax payable	$	4,082			908		$	4,990
Deferred revenue - current		46,230			6,767			52,997
Deferred revenue - long-term		223,781			12,584			236,365
Stockholders' Equity
Accumulated deficit		(262,489	)		(20,259	)		(282,748	)

The following tables summarize the impact of adopting ASC 606 on select unaudited condensed statement of operations line items (in thousands, except per share data):

	Three Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Revenue	$	10,895		$	1,614		$	12,509
Loss from operations		(24,791	)		1,614			(23,177	)
Loss before provision for income taxes		(22,543	)		1,614			(20,929	)
Provision for income taxes		2,650			(148	)		2,502
Net loss		(25,193	)		1,762			(23,431	)
Net loss per share, basic and diluted		(0.57	)		0.04			(0.53	)

	Nine Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Revenue	$	55,944		$	(7,913	)	$	48,031
Loss from operations		(44,151	)		(7,913	)		(52,064	)
Loss before provision for income taxes		(39,067	)		(7,913	)		(46,980	)
Provision for income taxes		4,483			908			5,391
Net loss		(43,550	)		(8,821	)		(52,371	)
Net loss per share, basic and diluted		(1.07	)		(0.22	)		(1.29	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of cash flows line items (in thousands):

	Nine Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Cash flows from operating activities:
Net loss	$	(43,550	)	$	(8,821	)	$	(52,371	)
Changes in operating assets and liabilities:
Accrued liabilities, income tax payable and other long-term liabilities		9,644			908			10,552
Deferred revenue		(34,726	)		7,913			(26,813	)

Recent Accounting Pronouncements

Basis of Presentation and Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2018

Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash

	As of September 30, 2018		As of December 31, 2017
Cash and cash equivalents	$	259,753	$	177,548
Restricted cash - non-current assets		917		917
Total	$	260,670	$	178,465

ASC 606

Summary Impact of Adopting ASC 606 on Select Unaudited Financial Statement Line Items

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed balance sheet line items (in thousands):

	As of September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Liabilities
Income tax payable	$	4,082			908		$	4,990
Deferred revenue - current		46,230			6,767			52,997
Deferred revenue - long-term		223,781			12,584			236,365
Stockholders' Equity
Accumulated deficit		(262,489	)		(20,259	)		(282,748	)

The following tables summarize the impact of adopting ASC 606 on select unaudited condensed statement of operations line items (in thousands, except per share data):

	Three Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Revenue	$	10,895		$	1,614		$	12,509
Loss from operations		(24,791	)		1,614			(23,177	)
Loss before provision for income taxes		(22,543	)		1,614			(20,929	)
Provision for income taxes		2,650			(148	)		2,502
Net loss		(25,193	)		1,762			(23,431	)
Net loss per share, basic and diluted		(0.57	)		0.04			(0.53	)

	Nine Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Revenue	$	55,944		$	(7,913	)	$	48,031
Loss from operations		(44,151	)		(7,913	)		(52,064	)
Loss before provision for income taxes		(39,067	)		(7,913	)		(46,980	)
Provision for income taxes		4,483			908			5,391
Net loss		(43,550	)		(8,821	)		(52,371	)
Net loss per share, basic and diluted		(1.07	)		(0.22	)		(1.29	)

The following table summarizes the impact of adopting ASC 606 on select unaudited condensed statement of cash flows line items (in thousands):

	Nine Months Ended September 30, 2018
	Balances Under ASC 605			Adjustments			As Reported Under ASC 606
Cash flows from operating activities:
Net loss	$	(43,550	)	$	(8,821	)	$	(52,371	)
Changes in operating assets and liabilities:
Accrued liabilities, income tax payable and other long-term liabilities		9,644			908			10,552
Deferred revenue		(34,726	)		7,913			(26,813	)

Fair Value Measurements and Short-Term Investments (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Short-Term Investments Subject to Fair Value Measurements on a Recurring Basis

		September 30, 2018
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	130,543	$	—	$	—		$	130,543
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. government bonds	Level I		204,990		—		(181	)		204,809
Total		$	336,450	$	—	$	(181	)	$	336,269

		December 31, 2017
	Valuation Hierarchy	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Aggregate Fair Value
Assets
Money market funds	Level I	$	164,440	$	—	$	—		$	164,440
Restricted cash (money market funds)	Level I		917		—		—			917
U.S. government bonds	Level I		196,629		—		(67	)		196,562
Total		$	361,986	$	—	$	(67	)	$	361,919

Accrued Liabilities (Tables)

9 Months Ended

Sep. 30, 2018

Accrued Liabilities Current [Abstract]

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	September 30,		December 31,
	2018		2017
Research and clinical expenses	$	14,846	$	10,068
Payroll and related expenses		4,823		4,526
Legal and professional expenses		1,328		1,523
Other accrued expenses		419		265
Total	$	21,416	$	16,382

Research and Collaboration Agreements (Tables)

9 Months Ended

Sep. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Summary of Contracts Assets and Liabilities

The following table presents changes in the Company’s total contract assets and liabilities during the nine months ended September 30, 2018 (in thousands):

			Additions				Deductions
	Balance at 12/31/2017		ASC 606 Adoption Adjustment		Adjustment to Transaction Price from Performance Obligation Satisfied		Revenue Recognized from an Adjustment to Transaction Price During the Period			Revenue Recognized from Amounts Included in Contract Liability at the Beginning of the Period			Balance at 9/30/2018
Contract liabilities:
Deferred revenue	$	305,263	$	10,912	$	21,000	$	(10,799	)	$	(37,014	)	$	289,362

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Activities Under Company's Stock Option Plans

Activities under the Company’s stock option plans for the nine months ended September 30, 2018 were as follows:

	Options Outstanding
	Number of Options			Weighted- Average Exercise Price Per Share
Balances at December 31, 2017		6,503,458		$	8.157
Options granted		1,921,900			25.760
Options exercised		(631,539	)		6.253
Option forfeited/expired		(111,764	)		17.248
Balances at September 30, 2018		7,682,055		$	12.586
Options exercisable at September 30, 2018		4,183,476		$	7.262

Total Stock-based Compensation Recognized

Total stock-based compensation recorded related to options granted to employees and non-employees and employee stock purchase plan was as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Stock-based compensation expense:
Research and development	$	2,131	$	1,267	$	5,989	$	3,813
General and administrative		2,282		1,514		6,273		4,724
Total stock-based compensation expense	$	4,413	$	2,781	$	12,262	$	8,537

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Options to purchase common stock		7,292,701		6,713,038		7,434,862		6,976,470
Total		7,292,701		6,713,038		7,434,862		6,976,470

Description of the Business - Additional Information (Detail) - Common Stock - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended
	Jul. 31, 2018	Sep. 30, 2018
Description of Business [Line Items]
Net proceeds from sale of common stock	$ 134,600
Underwriting discounts and commissions and offering expenses	$ 9,200	$ 9,154
Underwritten Public Offering
Description of Business [Line Items]
Issuance of common stock, shares	5,867,347
Common stock price, per share	$ 24.50
Underwriters
Description of Business [Line Items]
Issuance of common stock, shares	765,306

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($)
$ in Thousands

Sep. 30, 2018

Dec. 31, 2017

Sep. 30, 2017

Dec. 31, 2016

Cash And Cash Equivalents [Abstract]

Cash and cash equivalents

$ 259,753

$ 177,548

^[1]

Restricted cash

917

^[1]

Total

$ 260,670

$ 178,465

$ 285,142

$ 105,562

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)
$ in Thousands

Sep. 30, 2018

Jan. 01, 2018

Dec. 31, 2017

^[1]

Summary Of Significant Accounting Policies [Line Items]

Increase in accumulated deficit balance

$ (282,748)

$ (219,465)

Adjustments | ASC 606

Summary Of Significant Accounting Policies [Line Items]

Increase in accumulated deficit balance

$ (20,259)

$ (10,900)

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

Basis of Presentation and Summary of Significant Accounting Policies - Summary Impact of Adopting ASC 606 on Select Unaudited Condensed Balance Sheet Line Items (Details) - USD ($)
$ in Thousands

Sep. 30, 2018

Jan. 01, 2018

Dec. 31, 2017

^[1]

Liabilities

$ 4,990

$ 1

52,997

40,559

236,365

264,704

Stockholders' Equity

ASC 606 | Balances Under ASC 605

(282,748)

$ (219,465)

Liabilities

4,082

46,230

223,781

Stockholders' Equity

(262,489)

ASC 606 | Adjustments

Liabilities

908

6,767

12,584

Stockholders' Equity

Accrued Liabilities Current [Abstract]

$ (20,259)

$ (10,900)

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

Basis of Presentation and Summary of Significant Accounting Policies - Summary Impact of Adopting ASC 606 on Select Unaudited Condensed Statement of Operations Line Items (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 12,509	$ 24,144	$ 48,031	$ 44,550
Loss from operations	(23,177)	(11,025)	(52,064)	(45,012)
Loss before provision for income taxes	(20,929)	(10,266)	(46,980)	(43,713)
Provision for income taxes	2,502	(19)	5,391	7
Net loss	$ (23,431)	$ (10,247)	$ (52,371)	$ (43,720)
Net loss per share, basic and diluted	$ (0.53)	$ (0.28)	$ (1.29)	$ (1.19)
ASC 606 \| Balances Under ASC 605
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 10,895		$ 55,944
Loss from operations	(24,791)		(44,151)
Loss before provision for income taxes	(22,543)		(39,067)
Provision for income taxes	2,650		4,483
Net loss	$ (25,193)		$ (43,550)
Net loss per share, basic and diluted	$ (0.57)		$ (1.07)
ASC 606 \| Adjustments
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 1,614		$ (7,913)
Loss from operations	1,614		(7,913)
Loss before provision for income taxes	1,614		(7,913)
Provision for income taxes	(148)		908
Net loss	$ 1,762		$ (8,821)
Net loss per share, basic and diluted	$ 0.04		$ (0.22)

Basis of Presentation and Summary of Significant Accounting Policies - Summary Impact of Adopting ASC 606 on Select Unaudited Condensed Statement of Cash Flows Line Items (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (23,431)	$ (10,247)	$ (52,371)	$ (43,720)
Changes in operating assets and liabilities
Accrued liabilities, income tax payable and other long-term liabilities			10,552	4,124
Deferred revenue			(26,813)	$ 169,574
ASC 606 \| Balances Under ASC 605
Cash flows from operating activities:
Net loss	(25,193)		(43,550)
Changes in operating assets and liabilities
Accrued liabilities, income tax payable and other long-term liabilities			9,644
Deferred revenue			(34,726)
ASC 606 \| Adjustments
Cash flows from operating activities:
Net loss	$ 1,762		(8,821)
Changes in operating assets and liabilities
Accrued liabilities, income tax payable and other long-term liabilities			908
Deferred revenue			$ 7,913

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Fair Value Measurements and Investments - Schedule of Short-Term Investments Subject to Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 336,450	$ 361,986
Gross Unrealized Holding Losses	(181)	(67)
Aggregate Fair Value	336,269	361,919
Level I \| Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	130,543	164,440
Aggregate Fair Value	130,543	164,440
Level I \| Restricted cash (money market funds)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	917	917
Aggregate Fair Value	917	917
Level I \| U. S. government bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	204,990	196,629
Gross Unrealized Holding Losses	(181)	(67)
Aggregate Fair Value	$ 204,809	$ 196,562

Fair Value Measurements and Investments - Additional Information (Details)	Sep. 30, 2018 USD ($)
Fair Value Disclosures [Abstract]
Contractual maturities of longer than one year	$ 0

Accrued Liabilities - Summary of Accrued Liabilities (Details) - USD ($)
$ in Thousands

Sep. 30, 2018

Dec. 31, 2017

Research and clinical expenses

$ 14,846

$ 10,068

Payroll and related expenses

4,823

4,526

Legal and professional expenses

1,328

1,523

Other accrued expenses

419

265

Total

$ 21,416

$ 16,382

^[1]

[1]	The condensed balance sheet as of December 31, 2017 was derived from the audited financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017.

Research and Collaboration Agreements - AbbVie Ireland Unlimited Company - Additional Information (Details)	1 Months Ended			3 Months Ended			9 Months Ended
	May 31, 2018 USD ($)	Jul. 31, 2017 USD ($)	Apr. 30, 2016 USD ($) Agreement Target AccountingUnit	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2017 Target
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue				$ 289,362,000			$ 289,362,000		$ 305,263,000
License and Service
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized from collaborative arrangement				12,509,000		$ 23,662,000	48,031,000	$ 43,121,000
Seattle Genetics Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense fees paid	$ 4,000,000						4,000,000
AbbVie Ireland Unlimited Company
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment received	21,000,000
Revenue adjustment of milestone payment recognized					$ 9,900,000
AbbVie Ireland Unlimited Company \| ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment received			$ 14,000,000
Total transaction price			39,800,000
Estimated sublicense fees			$ 4,200,000
Number of accounting units \| AccountingUnit			2
AbbVie Ireland Unlimited Company \| License and Service
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized from collaborative arrangement				2,800,000		$ 15,400,000	16,300,000	$ 18,100,000
AbbVie Ireland Unlimited Company \| Up Front Payment Arrangement \| ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total transaction price			$ 30,000,000
AbbVie Ireland Unlimited Company \| Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of collaboration agreements \| Agreement			2
Percentage of net profits or net losses related to development costs			35.00%
Number of targets selected \| Target										1
Amount due from agreement				0			0		0
AbbVie Ireland Unlimited Company \| Collaborative Arrangement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets \| Target			2
AbbVie Ireland Unlimited Company \| CD71 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			$ 20,000,000
Milestone payment received	21,000,000	$ 14,000,000
Sublicense fees paid		$ 1,000,000
Accrued sublicense fees				$ 1,000,000			$ 1,000,000		500,000
Revenue recognition upon performance obligation, service period				5 years			5 years
Deferred revenue				$ 25,400,000			$ 25,400,000		11,200,000
AbbVie Ireland Unlimited Company \| CD71 Agreement \| ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			20,000,000
Total transaction price			29,800,000
Milestone payment received			$ 14,000,000
AbbVie Ireland Unlimited Company \| CD71 Agreement \| U.S
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Profit split on U.S. sales and royalties on ex U.S. sales			35.00%
AbbVie Ireland Unlimited Company \| CD71 Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments receivable upon achieving development, regulatory and commercial milestones			$ 470,000,000
AbbVie Ireland Unlimited Company \| Seattle Genetics Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense fees paid	$ 4,000,000
AbbVie Ireland Unlimited Company \| Seattle Genetics Agreement \| ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense fees paid			1,000,000
AbbVie Ireland Unlimited Company \| Discovery Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			10,000,000
Revenue recognition upon performance obligation			10,000,000
Estimated research service period							5 years
Deferred revenue				$ 5,200,000			$ 5,200,000		$ 6,800,000
AbbVie Ireland Unlimited Company \| Discovery Agreement \| ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received			10,000,000
AbbVie Ireland Unlimited Company \| Discovery Agreement \| Maximum \| Development, Regulatory and Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent milestone payments receivable			$ 275,000,000
AbbVie Ireland Unlimited Company \| Sublicense Agreement \| UC Regents
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment percentage			5.00%

Research and Collaboration Agreements - Amgen, Inc - Additional Information (Details)

1 Months Ended

3 Months Ended

9 Months Ended

Sep. 29, 2017

USD ($)

Target

Oct. 31, 2017

USD ($)

$ / shares

Sep. 30, 2018

USD ($)

$ / shares

Sep. 30, 2017

USD ($)

Sep. 30, 2018

USD ($)

$ / shares

Sep. 30, 2017

USD ($)

Mar. 31, 2018

USD ($)

Dec. 31, 2017

USD ($)

$ / shares

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Common stock, par value | $ / shares

$ 0.00001

Common stock, value of shares issued in connection with agreement

$ 134,596,000

Accrued liabilities

$ 21,416,000

21,416,000

$ 16,382,000

^[1]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

289,362,000

305,263,000

License and Service

Revenue recognized from collaborative arrangement

12,509,000

$ 23,662,000

48,031,000

$ 43,121,000

Amgen Inc | EGFR Products

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Amgen Inc | Amgen Other Products

41,000,000

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreement

4,000,000

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Amount due from agreement

Collaboration and License Agreement | EGFR Products

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration and License Agreement | License and Service

41,000,000

45,300,000

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Revenue recognized from collaborative arrangement

1,500,000

$ 0

4,400,000

$ 0

Collaboration and License Agreement | Amgen Other Products

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]