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 * Canaan IX L.P.   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 __X__ 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) 10/11/2016 (Street) WESTPORT, CT 06880 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ 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 10/11/2016   J(1)   300,000 D (1) 3,944,381 I See Footnote (2)

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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
Canaan IX L.P. 285 RIVERSIDE AVENUE, SUITE 250 WESTPORT, CT 06880	X	X
Canaan Partners IX LLC 285 RIVERSIDE AVENUE, SUITE 250 WESTPORT, CT 06880	X	X

Signatures

Canaan IX L.P., By: Canaan Partners IX LLC, its general partner, By: /s/ Nancy Levenson, Attorney-in-Fact		10/12/2016
**Signature of Reporting Person		Date
Canaan Partners IX LLC, By: /s/ Nancy Levenson, Attorney-in-Fact		10/12/2016
**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 October 11, 2016, Canaan IX L.P. (the "Canaan Fund") distributed, for no consideration, 300,000 shares of Common Stock of the issuer (the "Shares") to its limited partners and to Canaan Partners IX LLC ("Canaan IX" and, together with the Canaan Fund, the "Canaan Entities"), the general partner of the Canaan Fund, representing each such partner's pro rata interest in the shares held by the Canaan Fund. On the same date, Canaan IX distributed, for no consideration, the Shares it received from the distribution to its members in an amount equal to each such member's pro rata interest in the Shares. The aforementioned distributions were made in accordance with the exemptions afforded by Rule 16a-13 and Rule 16a-9 of the Securities Exchange Act of 1934, as amended.
(2)	The shares are held directly by the Canaan Fund. Canaan IX, is the sole general partner of the Canaan Fund, and each may be deemed to have sole voting, investment and dispositive power with respect to the shares held by the Canaan Fund. Timothy Shannon, a non-managing member of Canaan IX, serves as representative of the Canaan Entities on the issuer's board of directors. Canaan IX disclaims Section 16 beneficial ownership of the securities held by the Canaan Fund, except to the extent of its pecuniary interest therein, if any.
Remarks: Exhibit 24 - Power of Attorney filed herewith

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