Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
McCarthy Sean A.
   2. Issuer Name and Ticker or Trading Symbol
CytomX Therapeutics, Inc. [CTMX] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
President and CEO
(Last)
(First)
(Middle)
343 OYSTER POINT BLVD., SUITE 100		 3. Date of Earliest Transaction (Month/Day/Year)
09/26/2016
(Street)

SOUTH SAN FRANCISCO, CA 94080		 4. If Amendment, Date Original Filed(Month/Day/Year)
 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)		 4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		 5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)		 6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)		 7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)		 5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)		 6. Date Exercisable and Expiration Date
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(Instr. 3 and 4)		 8. Price of Derivative Security
(Instr. 5)		 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)		 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)		 11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (Right to Buy) $ 0.945 09/26/2016   A   48,379     (1) 02/25/2023 Common Stock 48,379 $ 0 48,379 D  
Stock Option (Right to Buy) $ 1.5749 09/26/2016   A   122,424     (2) 02/08/2025 Common Stock 122,424 $ 0 122,424 D  

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
McCarthy Sean A.
343 OYSTER POINT BLVD.
SUITE 100
SOUTH SAN FRANCISCO, CA 94080		   X     President and CEO  

Signatures

 /s/ Cynthia J. Ladd, as Attorney-in-Fact for Sean A. McCarthy   09/28/2016
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) On February 26, 2013, the Reporting Person was granted an option to purchase 96,758 shares of Common Stock, as adjusted for the 1-for-62.997 reverse stock split effected prior to the Issuer's initial public offering, to vest in two equal tranches upon achievement of certain performance-based milestones (the "Performance Option"). 50% of the Performance Option previously vested upon achievement of the first performance milestone. On September 26, 2016, the second performance milestone was achieved resulting in vesting of the remaining 50% of the Performance Option.
(2) On February 9, 2015, the Reporting Person was granted an option to purchase 122,424 shares of Common Stock, as adjusted for the 1-for-62.997 reverse stock split effected prior to the Issuer's initial public offering, to vest in full upon achievement of a certain performance-based milestone (the "Performance Option"). On September 26, 2016, the performance milestone was achieved resulting in 100% of the Performance Option vesting.

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