In June 2020, the Company’s board of directors adopted, and the Company’s shareholders approved the 2020 Employee Share Purchase Plan (the “ESPP”). The maximum number of common shares that may be issued under the ESPP was initially 327,000. Additionally, the number of shares reserved and available for issuance under the ESPP automatically increases each January 1, beginning on January 1, 2021 and each January 1 thereafter through January 31, 2030, by the lesser of (1) 1.0% of the total number of common shares outstanding on December 31 of the preceding calendar year, (2) 3,300,000 common shares, or (3) such smaller number of common shares as the Company’s board of directors may designate. As of March 31, 2021, the number of common shares that may be issued under the ESPP is 696,029.

The ESPP enables eligible employees to purchase common shares of the Company at the end of each offering period at a price equal to 85% of the fair market value of the shares on the first business day or the last business day of the offering period, whichever is lower. Participation in the ESPP is voluntary. Eligible employees become participants in the ESPP by enrolling in the plan and authorizing payroll deductions. At the end of each offering period, payroll deductions that have accumulated are used to purchase shares of the Company’s shares at the discounted price. The Company makes no contributions to the ESPP. A participant may withdraw from the ESPP or suspend contributions to the ESPP. If the participant elects to withdraw during an offering, all contributions are refunded as soon as administratively practicable. If a participant elects to withdraw or suspend contributions, they will not be able to re-enroll in the current offering but may elect to participate in future offerings. The ESPP purchases only whole shares of the Company’s shares. The Company’s first ESPP offering period began February 16, 2021 and will end on August 15, 2021. Subsequent offering periods will be on a rolling six-month basis.

As of March 31, 2021, no common shares have been issued under the ESPP. A total of $0.03 million and nil of share-based compensation expense was recorded in operating expenses in the three months ended March 31, 2021 and 2020, respectively.

In December 2016, as further amended in December 2017 and September 2019, the Company adopted the Repare Therapeutics Inc. Option Plan (the “Option Plan”) for the issuance of share options and other share-based awards to directors, officers, employees or consultants. The Option Plan authorized up to 4,074,135 shares of the Company’s common shares to be issued.

In June 2020, the Company’s board of directors adopted, and the Company’s shareholders approved the 2020 Equity Incentive Plan (the “2020 Plan”). The 2020 Plan became effective on the effective date of the IPO, at which time the Company ceased granting awards under the Option Plan. The 2020 Plan allows the Company’s compensation committee to grant equity-based and cash-based incentive awards to the Company’s officers, employees, directors and consultants. A total of 3,600,000 common shares were initially reserved for issuance under the 2020 Plan, plus the number of shares (not to exceed 3,807,448 shares) consisting of (i) 298,605 common shares that were available for the issuance of awards under the Option Plan at the time the 2020 Plan became effective, which ceased to be available for future issuance under the Option Plan at such time and (ii) any shares subject to outstanding options or other share awards that were granted under the Option Plan that terminate or expire prior to exercise or settlement; are forfeited because of the failure to vest; or are reacquired or withheld (or not issued) to satisfy a tax withholding obligation or the purchase or exercise price. In addition, the number of shares reserved and available for issuance under the 2020 Plan automatically increases each January 1, beginning on January 1, 2021 and each January 1 thereafter through January 1, 2030, by 5% of the outstanding number of common shares on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s board of directors. As of March 31, 2021, the number of common shares reserved for issuance under the 2020 Plan is 5,789,592.

	2021					2020
	Number of shares			Weighted average exercise price		Number of shares			Weighted average exercise price
Outstanding at beginning of period		4,132,123		$	6.39		3,505,119		$	2.07
Granted		1,141,726		$	36.50		—		$	—
Exercised		(87,786	)	$	2.09		(181,318	)	$	1.79
Cancelled or forfeited		(10,828	)	$	8.78		—		$	—
Outstanding at end of period		5,175,235		$	13.10		3,323,801		$	2.09

During the three months ended March 31, 2021, an aggregate of 87,786 options were exercised at a weighted-average exercise price of $2.09 per share, for aggregate proceeds of $0.2 million. As a result, an amount of $0.1 million previously included in additional paid-in capital related to the exercised options has been credited to common shares and deducted from additional paid-in capital.

	Three Months Ended March 31,
	2021		2020
	(in thousands)
Research and development	$	987	$	133
General and administrative		1,070		138
Total share-based compensation expense	$	2,057	$	271

The grant date fair value of stock options granted during the three-months ended March 31, 2021 was $23.83 per option. The assumptions that the Company used in the Black Scholes option-pricing model to determine the grant date fair value of stock options granted to employees and non-employees were as follows, presented on a weighted average basis:

	Three Months Ended March 31,
	2021			2020
Risk-free interest rate		0.67	%		—
Expected terms (in years)		6.08			—
Expected volatility		75.41	%		—
Expected dividend yield		0.00	%		—

As of March 31, 2021, there was $38.8 million of unrecognized share-based compensation expense related to unvested stock options to be recognized over a weighted average period of 2.7 years.