X0306 4 2016-06-02 0 0001501989 CytomX Therapeutics, Inc. CTMX 0001538676 Canaan IX L.P. 285 RIVERSIDE AVENUE, SUITE 250 WESTPORT CT 06880 1 0 1 0 0001654586 Canaan Partners IX LLC 285 RIVERSIDE AVENUE, SUITE 250 WESTPORT CT 06880 1 0 1 0 Common Stock 2016-06-02 4 S 0 41193 10.79 D 4422734 I See Footnote Common Stock 2016-06-03 4 S 0 18428 10.83 D 4404306 I See Footnote The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $10.55 - $11.09, inclusive. The reporting persons undertake 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 (1) of this Form 4. The shares are held directly by Canaan IX L.P. (the "Canaan Fund"). Canaan Partners IX LLC ("Canaan IX" and together with the Canaan Fund, the "Canaan Entities") 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. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $10.585 - $11.08, inclusive. The reporting persons undertake 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. Exhibit 24 - Power of Attorney (incorporated by reference to the Power of Attorney filed as Exhibit 24 to the Form 4 filed by the Reporting Persons on October 7, 2015) Canaan IX L.P., By: Canaan Partners IX LLC, its general partner, By: /s/ Jaime Slocum, Attorney-in-Fact 2016-06-06 Canaan Partners IX LLC, By: /s/ Jaime Slocum, Attorney-in-Fact 2016-06-06