X0306 4 2023-02-15 0 0001718852 Prometheus Biosciences, Inc. RXDX 0001714828 Marshall Keith W C/O PROMETHEUS BIOSCIENCES, INC. 3050 SCIENCE PARK ROAD SAN DIEGO CA 92121 0 1 0 0 Chief Financial Officer Common Stock 2023-02-15 4 M 0 5000 3.70 A 14811 D Common Stock 2023-02-15 4 S 0 5000 119.38 D 9811 D Stock Option (Right to Buy) 3.70 2023-02-15 4 M 0 5000 0.00 D 2030-12-17 Common Stock 5000 113040 D The transactions reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the Reporting Person. The price reported in Column 4 is a weighted average price. 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. 25% of the shares subject to the option vested and became exercisable on November 5, 2021, and 1/48th of the shares subject to the option shall vest monthly thereafter, subject to the Report Person's continued service with the Issuer through each vest date. /s/ Timothy K. Andrews, attorney-in-fact for Keith W. Marshall 2023-02-17