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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1. Name and Address of Reporting Person * SHANNON TIMOTHY M   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 _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 285 RIVERSIDE AVENUE, SUITE 250 3. Date of Earliest Transaction (Month/Day/Year) 05/25/2016 (Street) WESTPORT, CT 06880 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 Common Stock 05/25/2016   S   11,456 D $ 10.02 (2) 4,551,359 I (1) See Footnote (1) Common Stock 05/26/2016   S   39,887 D $ 10.43 (3) 4,511,472 I (1) See Footnote (1) Common Stock               134 D

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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

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
SHANNON TIMOTHY M 285 RIVERSIDE AVENUE SUITE 250 WESTPORT, CT 06880	X

Signatures

By: /s/ Cynthia J. Ladd, Attorney-in-Fact		05/27/2016
**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)	These shares of Common Stock ("Shares") are held directly by Canaan IX L.P. The Reporting Person is a non-managing member of Canaan Partners IX LLC, the general partner of Canaan IX L.P. The Reporting Person does not have voting, investment or dispositive power over any of the Shares directly held by Canaan IX L.P. and disclaims beneficial ownership of the Shares except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that the Reporting Person is the beneficial owner of the Shares for purposes of Section 16 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or for any other purpose.
(2)	The price reported in Column 4 is a weighted average price. These Shares were sold in multiple transactions at prices ranging from $10.00 - $10.085, inclusive. The Reporting Person undertakes to provide to the issuer, any security holder of the issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of Shares sold at each separate price within the range set forth in footnote (2) of this Form 4.
(3)	The price reported in Column 4 is a weighted average price. These Shares were sold in multiple transactions at prices ranging from $10.00 - $10.74, inclusive. The Reporting Person undertakes to provide to the issuer, any security holder of the issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of Shares sold at each separate price within the range set forth in footnote (3) of this Form 4.
Remarks: Exhibit 24 - Power of Attorney (incorporated by reference to the Power of Attorney filed as Exhibit 24.1 to the Form 3 filed by the Reporting Person on October 7, 2015)

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