v3.26.1
Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Jun. 30, 2025
Cover [Abstract]    
Document Type 10-K  
Amendment Flag false  
Document Period End Date Dec. 31, 2025  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus FY  
Trading Symbol CTMX  
Entity Registrant Name CytomX Therapeutics, Inc.  
Entity Central Index Key 0001501989  
Current Fiscal Year End Date --12-31  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
ICFR Auditor Attestation Flag true  
Entity Shell Company false  
Entity File Number 001-37587  
Entity Tax Identification Number 27-3521219  
Entity Address, Address Line One 151 Oyster Point Boulevard,  
Entity Address, Address Line Two Suite 400  
Entity Address, City or Town South San Francisco  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94080  
City Area Code 650  
Local Phone Number 515-3185  
Entity Interactive Data Current Yes  
Title of 12(b) Security Common Stock, $0.00001 par value  
Security Exchange Name NASDAQ  
Entity Incorporation, State or Country Code DE  
Document Annual Report true  
Document Transition Report false  
Entity Public Float   $ 372.3
Entity Common Stock, Shares Outstanding 170,186,742  
Documents Incorporated by Reference

Portions of the registrant’s definitive proxy statement to be filed for its 2026 Annual Meeting of Stockholders are incorporated by reference into Part III hereof. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the end of the fiscal year covered by this Annual Report on Form 10-K.

  
Auditor Name Ernst & Young LLP  
Auditor Firm Id 42  
Auditor Location San Francisco, California  
Document Financial Statement Error Correction [Flag] false  
Auditor Opinion [Text Block]

Opinion on the Financial Statements

We have audited the accompanying balance sheets of CytomX Therapeutics, Inc. (the Company) as of December 31, 2025 and 2024, the related statements of operations and comprehensive income (loss), stockholders’ equity (deficit) and cash flows for each of the two years in the period ended December 31, 2025, and the related notes (collectively referred to as the “financial statements”). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company at December 31, 2025 and 2024, and the results of its operations and its cash flows for each of the two years in the period ended December 31, 2025, in conformity with U.S. generally accepted accounting principles.

We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the Company's internal control over financial reporting as of December 31, 2025, based on criteria established in Internal Control–Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 framework), and our report dated March 16, 2026 expressed an unqualified opinion thereon.