X0306 4 2018-06-13 0 0001501989 CytomX Therapeutics, Inc. CTMX 0001184126 GLUCK FREDERICK W 743 SAN YSIDRO ROAD SANTA BARBARA CA 91308 1 0 0 0 Common Stock 271643 I By Frederick W. Gluck 1997 Family Trust dtd July 28, 1997 Common Stock 22111 I By Richlin Partners, LLC Common Stock 3200 I By Spouse Stock Option (Right to Buy) 25.25 2018-06-13 4 A 0 14000 0.00 A 2028-06-12 Common Stock 14000 14000 D The Reporting Person is a trustee of Frederick W. Gluck 1997 Family Trust dtd July 28, 1997. Richlin Partners, LLC is an entity owned of record by the spouse of the Reporting Person. The underlying shares subject to the option vest and become exercisable as to 100% of the total number of shares subject to the option on the earlier of (i) the first anniversary of the grant date or (ii) the date of the 2019 Annual Meeting of the Issuer's stockholders, assuming continuous service as a director until such vesting date. /s/ Debanjan Ray, as Attorney-in-Fact for Frederick W. Gluck 2018-06-15