X0306 4 2020-06-25 0 0001805890 Fusion Pharmaceuticals Inc. FUSN 0001609405 Khuong Chau Quang C/O FUSION PHARMACEUTICALS INC. 270 LONGWOOD ROAD SOUTH HAMILTON A6 L8P 0A6 ONTARIO, CANADA 1 0 0 0 Warrants to Purchase Class B Preferred Shares 1.1514 2020-01-10 4 A 0 359377 0.00 A 2020-01-10 2022-01-10 Common Shares 67311 359377 I See Footnote Class B Preferred Shares 2020-06-02 4 P 0 5939025 1.1514 A Common Shares 1112385 11878051 I See Footnote Stock Option (Right to Buy) 17.00 2020-06-25 4 A 0 30000 0.00 A 2030-06-18 Common Shares 30000 30000 D Upon the closing of the Issuer's initial public offering, the Warrants to purchase Class B Preferred Shares will become warrants to purchase Common Shares at an exercise price of $8.10 per share. OrbiMed Capital GP VII LLC ("GP VII") is the general partner of OrbiMed Private Investments VII, LP ("OPI VII"). OrbiMed Advisors LLC ("OrbiMed Advisors") is the managing member of GP VII. By virtue of such relationships, GP VII and OrbiMed Advisors may be deemed to have voting and investment power with respect to the shares held by OPI VII and as a result may be deemed to have beneficial ownership of such shares. The Reporting Person is an employee of OrbiMed Advisors. OrbiMed Advisors exercises investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho and Jonathan T. Silverstein. Each of GP VII, OrbiMed Advisors and the Reporting Person disclaims beneficial ownership of the shares held by OPI VII, except to the extent of its or his pecuniary interest therein, if any. The Class B Preferred Shares are convertible into Common Shares on a one-for-5.339 basis. Upon the closing of the Issuer's initial public offering, the Class B Preferred Shares will convert into the number of Common Shares shown in column 7. The Class B Preferred Shares have no expiration date. This option shall vest and become exercisable in 36 equal monthly installments commencing on July 18, 2020. /s/ John Crowley, Attorney-in-Fact 2020-06-29