X0306 4 2018-06-13 0 0001501989 CytomX Therapeutics, Inc. CTMX 0001270928 SCARLETT JOHN A C/O GERON CORPORATION 149 COMMONWEALTH DRIVE, SUITE 2070 MENLO PARK CA 94025 1 0 0 0 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 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 John A. Scarlett 2018-06-15