X0306 4 2021-05-20 0 0001808158 Repare Therapeutics Inc. RPTX 0001477123 Segal Lloyd Mitchell C/O REPARE THERAPEUTICS INC. 7210 FREDERICK-BANTING, SUITE 100 ST-LAURENT A8 H4S 2A1 QUEBEC, CANADA 0 1 0 0 President and CEO Common Stock 2021-05-20 4 S 0 3770 35.0306 D 133584 I See Footnote Common Stock 5000 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 31, 2020. These securities are registered in the name of Arvala Inc. (f/k/a 3996953 Canada Inc., the "Company"). The Reporting Person is the sole stockholder of the Company. /s/ Steve Forte, Attorney-in-Fact 2021-05-21