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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , D.C. 20549 FORM 10 - K ( Mark One ) ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR Title of each class Common Stock , $ 0.00001 par value For the transition period from Delaware ( State or other jurisdiction of incorporation or organization ) Large accelerated filer Non - accelerated filer to Commission File Number 001-37587 CytomX Therapeutics , Inc. ( Exact Name of Registrant as Specified in Its Charter ) 151 Oyster Point Boulevard , Suite 400 South San Francisco , California ( Address of principal executive offices ) ( 650 ) 515-3185 ( Registrant's telephone number , including area code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) CTMX Securities registered pursuant to Section 12 ( g ) of the Act : None 27-3521219 ( I.R.S. Employer Identification No. ) 94080 ( Zip Code ) Name of each exchange on which registered The Nasdaq Global Select Market No X No > Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes Indicate by check mark whether the issuer ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No Indicate by check mark whether the registrant has submitted electronically , every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Accelerated filer Smaller reporting company Emerging growth company X | ■ If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No As of June 30 , 2020 , the last business day of the registrant's most recently completed second fiscal quarter , the aggregate market value of the registrant's common stock held by non - affiliates of the registrant was approximately $ 379.4 million , based on the closing price of the registrant's common stock on the Nasdaq Global Select Market on June 30 , 2020 of $ 8.33 per share . Shares of the registrant's common stock held by each officer and director and each person known to the registrant to own 10 % or more of the outstanding common stock of the registrant have been excluded in that such persons may be deemed affiliates . This determination of affiliate status is not a determination for other purposes . As of February 2 , 2021 , 64,784,355 shares of the registrant's common stock , $ 0.00001 par value per share , were outstanding . DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant's definitive proxy statement to be filed for its 2021 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 .