PRIVATE AND CONFIDENTIAL October 21, 2019 Katina Dorton [ADDRESS] Dear Katina:

Separation Payments and Benefits. As consideration for you signing this Separation Agreement and the attached full and final release:

Subject to the conditions set forth in this Separation Agreement, the Company will pay you a Severance Amount of $354,375, reduced dollar-for-dollar by the fees paid to you during the consulting period referenced in the attached Independent Contractor Agreement dated of even date herewith.

Subject to the conditions set forth in this Separation Agreement and in accordance with section 6.2(c) of your Employment Agreement, if you timely elect COBRA health continuation coverage, then the Company will pay you a monthly cash payment equal to the monthly (or more frequent) employer contribution that the Company would have made to provide health insurance to you under the Company’s group health plan had you remained employed with the Company for nine months or your COBRA health continuation period, whichever ends earlier. This monthly payment in respect of medical and dental benefits is $1,798.98 and the monthly payment for vision benefits is currently estimated at $10 and the actual amount will be communicated to you after the Company receives an invoice for its employer contributions that includes you as a participant in the vision benefits plan.

The amounts payable under (a) and (b) above will be paid in substantially equal installments in accordance with the Company’s payroll practices over nine months following the Separation Date. The first installment will be made on the first payroll date following the expiration of the Revocation Period (as defined in the attached release) and will include a catch-up payment to cover amounts retroactive to the day immediately following the Separation Date.

Subject to the conditions set forth in this Separation Agreement and in accordance with section 6.2(b) of your Employment Agreement and the terms of your option grant agreement, 393,750 of your 1,350,000 stock options to acquire common shares of Repare Therapeutics Inc. (“Repare”) will become immediately vested and remain exercisable for six months following the Separation Date. The remaining 956,250 stock options will immediately be forfeited on the Separation Date. The exercise of vested stock options is subject to the terms and conditions of the Repare Therapeutics Inc. Option Plan, including the requirement to agree to be bound by Repare’s shareholders agreement.

Group Benefits. All group benefit coverage will cease on the Separation Date. You will be provided with information regarding COBRA health continuation coverage. If you wish, you may exercise conversion options, at your own expense, to convert some of your group coverage to an individual policy when your group coverage ends. You should contact [NAME] at [PHONE NUMBER] immediately for details regarding this conversion option, as there may be time limits for these conversion options. The Company recommends that you take whatever steps you feel appropriate to obtain replacement benefit coverage when your existing coverage expires.

Annual Bonus. You acknowledge and agree that you do not qualify for an Annual Bonus for 2019.

Indemnification. The Company will continue to provide you with directors’ and officers’ liability insurance coverage and indemnification in accordance with section 4.9 of your Employment Agreement.

Tax Equalization Payments. You will be entitled to receive tax equalization payments, to the extent applicable, in accordance with section 4.6 of your Employment Agreement.

Return of Company Property. You shall promptly return all Company property, including computer and other electronic equipment, keys or passes, literature, files and other documentation, software, and passwords as soon as reasonably practicable following your return from a scheduled vacation on or about October 29, 2019. The Company will provide you with an electronic copy of your calendar and contact list.

Post-Employment Covenants. You acknowledge and agree that you will continue to be subject to post-employment obligations regarding confidentiality, non-solicitation and non-disparagement set forth in sections 10, 11 and 13 of your Employment Agreement and that the remedies set forth in section 6.2(a) and 15 of your Employment Agreement will continue to be available to the Company. The Company acknowledges and agrees that it

Cooperation. You agree to cooperate with the Company following your Separation Date as set forth in section 9 of your Employment Agreement. You also agree to enter into the consulting agreement attached as schedule B hereto.

Statutory Compliance. All payments under this Separation Agreement are expressed in United States currency and subject to withholding taxes and statutory or authorized deductions.

No Admission of Liability. You understand and agree that nothing in this Separation Agreement or in the attached release shall be deemed an admission of liability on the part of the Company, and, in fact, such liability is specifically denied.

Release Form. All payments and benefits set forth in paragraph 1 of this Separation Agreement are conditional upon you signing, in the presence of a witness, a copy of both this Separation Agreement and the full and final release attached as Schedule A and returning original signed copies of both to me by no later than 5:00 PM on November 11, 2019.

Entire Agreement. This Separation Agreement and the attachments hereto constitute the entire agreement between you and the Company with respect to the subject matter herein and supersedes and replaces any and all previous agreements, written or oral, express or implied. Any modifications or amendments to this Separation Agreement or any of the attachments hereto must be in writing and signed by both parties or else they shall have no force and effect.

Severability. If any provision in this Separation Agreement is hereafter construed to be invalid or unenforceable, the same shall not affect the remaining provisions of this Separation Agreement, which shall be given full effect, without regard to the invalid provision, and any court having jurisdiction shall have the power to rewrite the offending provision, delete any or all of the offending provision, add additional language to this Separation Agreement or make such other modifications as it deems warranted to carry out the intent and agreement of the parties as embodied herein to the maximum extent permitted by applicable law.

Enurement. This Separation Agreement shall enure to the benefit of and be binding upon you and your respective successors and assigns, including without limitation, your heirs, executors, administrators and personal representatives.

Governing Law. The Separation Agreement shall be governed by the laws of the Commonwealth of Massachusetts, without regards to its conflict of laws principles.

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Except for the rights and obligations created by the Separation Agreement, I, for and on behalf of myself and my past and present spouse(s), agents, heirs, executors, administrators and assigns, hereby release, acquit and forever discharge Repare Therapeutics USA Inc. (the “Company”), Repare Therapeutics Inc., and their respective past and present parent companies, subsidiaries, affiliates and related companies, as well as their respective current and former officers, directors, agents, trustees, shareholders, insurers, assigns, representatives, and attorneys, and each of them, both in their individual and representative capacities, (collectively, the “Released Parties”), to the fullest extent permitted by law, from any and all claims, demands, grievances, causes of action and rights of appeal (“Claims”), whether known and unknown, that I had, have or may have against any of them and that are based upon acts, omissions or events that occurred on or before the Effective Date (as defined below) relating to my employment with the Company or termination therefrom, including, but not limited to:

all Claims under Title VII of the Civil Rights Act of 1964, 42 U.S.C. s. 2000e, the Americans with Disabilities Act, 42 U.S.C. s. 12101, et seq., the Age Discrimination in Employment Act, 29 U.S.C. s. 621, et seq. (“ADEA”), the Worker Adjustment and Retraining Notification Act, 29 U.S.C. s. 210, et seq., the Family Medical Leave Act, the Fair Credit Reporting Act, 15 U.S.C. § 1681 et seq., and the Employee Retirement Income Security Act of 1974 (“ERISA”), 29 U.S.C. § 1001 et seq., all as amended;

all Claims, whether in tort, contract, by statute, or on any other basis, whether in law or in equity, whether civil, criminal or administrative, whether known or unknown, for damages or monies owed by Releasees, including compensatory damages, emotional distress damages, physical injury damages, punitive damages, attorney’s fees, costs, and interest, including all Claims for back pay, overtime pay, severance pay, notice pay, health benefits, retirement benefits, all other benefits, vacation pay, holiday pay, sick pay, commissions, bonuses, relocation expenses, loans, expense reimbursements, or other monies due. I acknowledge and agree that, except as set forth herein, I have received payment in full for all services rendered to the Company prior to the Separation Date, including, but not limited to, all wages, vacation pay, sick leave, bonuses, and any other employment compensation or fringe benefit, and I hereby release the Company and the Released Parties from any such claims;

all Claims under the Massachusetts Employment Practices Law, the Massachusetts Civil Rights Act, the Massachusetts Equal Rights Act, the Massachusetts Wage Act, the Massachusetts Equal Pay Act, and any other state, federal, city, county or local statute, rule, regulation, ordinance or order, or the national or local common law of any jurisdiction located within or outside the United States of America that relates to employers, employees or the workplace;

any Claim for future consideration for employment with the Company, any claims for attorneys’ fees and costs and any employment rights or entitlement law, and any claims for wrongful discharge, intentional infliction of emotional distress, defamation, libel or slander, payment of wages, outrageous behavior, breach of contract or any duty allegedly owed to me, discrimination based upon race, color, ethnicity, sex, age, national origin, religion, disability, sexual orientation, or another unlawful criterion or circumstance, and any other theory of recovery.

As part of the general release set out above, I specifically agree that I hereby release, remise and forever discharge the Company and the Released Parties, and each of them, both in their individual and representative capacities, from any and all Claims, both known and unknown, arising under the ADEA that I had, have or may have against any of them and that are based upon acts, omissions or events that occurred on or before the Effective Date. I understand and acknowledge the significance and consequences of this specific waiver of any ADEA Claims, have received or have had the opportunity to receive independent legal advice from my attorneys regarding this waiver, and hereby assume full responsibility for any damage, loss or liability which I may hereafter incur by reason of such waiver.

It is the intention of the parties to make this release as broad and as general as the law permits. This Release does not prevent me from enforcing my non-forfeitable rights to accrued benefits (within the meaning of Sections 203 and 204 of the Employee Retirement Income Security Act of 1974, as amended) under applicable retirement plans, unemployment insurance benefits, workers’ compensation Claims, or other Claims that cannot legally be waived. Further, nothing herein prevents me from interacting with or filing a charge with, as authorized by law, the EEOC or any other bona fide government agency; however, I will not seek or be entitled to any personal recovery in any action or proceeding that may be commenced on my behalf arising out of the matters released hereby.

Representations and Warranties

I represent and warrant that I do not have any lawsuit, claim, charge, grievance or complaint (each an “Action”) against the Company or any of the Released Parties pending in any forum, based upon acts, omissions or events occurring prior to the Effective Date of this Release, that I will not at any time hereafter file any Action against the Company or any of the Released parties in any forum.

Representations re Waiver of ADEA Claims: As required by the ADEA, I understand, represent, warrant and agree that:

I was advised (and am hereby advised) in writing to consider the terms of this Release and to consult with an attorney of my choice prior to executing this Release;

prior to executing this Release, I had the opportunity to consider this Release for an amount of time that I considered to be reasonable;

I knowingly and voluntarily agree to all of the terms set forth in this Release;

I am executing this Release in exchange for good and valuable consideration; and

I knowingly and voluntarily intend to be legally bound by this Release.

Consideration Period

I acknowledge that I have been afforded at least 21 days to consider the meaning and effect of this Release and any changes to this Release or the Separation Agreement, whether material or immaterial, do not restart the running of the 21 day consideration period. If I sign this Release, the 7-day Revocation Period described below will begin after I have signed this Release.

I acknowledge and agree that if I execute this Release prior to the expiration of 21 days after my receipt thereof, and/or choose to forego seeking the advice of independent legal counsel, I do so freely, and I knowingly waive any and all future claims that such action(s) would affect the validity of this Release.

Revocation Period: I have the right to revoke this Release within 7 days of signing it (“Revocation Period”). To revoke this Release, I must send a written letter by overnight delivery, personal delivery or registered mail to: Repare Therapeutics Inc., Attn: ▇▇▇▇▇ ▇▇▇▇▇, ▇▇▇▇ ▇▇▇▇▇▇▇▇▇-▇▇▇▇▇▇▇, ▇▇▇▇▇ ▇▇▇, ▇▇. ▇▇▇▇▇▇▇, ▇▇ ▇▇▇ ▇▇▇.

This Release is binding upon me and my past and present spouse(s), agents, heirs, executors, administrators, and assigns and shall inure to the benefit of the Company and the Released Parties.

This Release and the Separation Agreement constitute the complete understanding between me and the Company and supersede all other agreements not specifically reaffirmed in those agreements. No other promises or agreements will be binding unless signed by me and the Company.

This Release shall be effective on the date on which I sign this Release, but no sooner than my last day of employment (the “Effective Date”), and shall become irrevocable upon expiration of the Revocation Period described above.

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22/10/2019

TERM OF AGREEMENT

SERVICES TO BE PROVIDED

FEES

HOURS OF WORK

INDEPENDENT CONTRACTOR

SEVERABILITY

CHANGES TO AGREEMENT

ENUREMENT

ASSIGNMENT

ENTIRE AGREEMENT

GOVERNING LAW

EXPENSES