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Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense is recognized for stock options granted to employees and non-employees and has been reported in the Company’s condensed consolidated condensed statements of operations as follows:

		Three Months Ended March 31,
		2019				2018
Research and development		$	277			$	625
General and administrative			386				556
Total stock-based compensation expense		$	663			$	1,181

Summary of Stock Option Activity

The following table summarizes stock option activity under the Plans:

		Shares Available for Grant				Number of Options Outstanding				Weighted- Average Exercise Price per Option				Weighted- Average Remaining Contract Term				Aggregate Intrinsic Value
																		(In thousands)
Outstanding, December 31, 2018			1,350,582				1,122,677			$	11.63				9.22
Shares reserved for issuance			1,122,213
Options granted(1)			(604,440	)			604,440				8.58
Options cancelled			20,800				(20,800	)			9.91
Outstanding, March 31, 2019			1,889,155				1,706,317				10.57				9.30			$	627
Exercisable, March 31, 2019							194,221				11.62				8.70				202
Vested and expected to vest, March 31, 2019							1,706,317				10.57				9.30				627

(1) The Company granted 9,840 stock options to non-employees during the three months ended March 31, 2019.

Schedule of Assumptions to Estimate Fair Value of Stock Options for Employees and Non-Employees Using Black-Scholes Option Pricing Model

The fair value of stock options for employees and non-employees was estimated using a Black-Scholes option pricing model with the following assumptions:

		Three Months Ended March 31,
		2019				2018
Employees:
Fair value of common stock		$8.53 - $8.90				$13.17 - $15.45
Expected term (in years)			6.1			5.8 - 6.6
Expected volatility		93.7% - 94.8%				76.1% - 77.7%
Risk-free interest rate		2.5% - 2.6%				2.4% - 2.7%
Expected dividend yield		0.0%				0.0%
Non-employees:
Fair value of common stock		$6.82 - $8.61				$9.58 - $15.45
Expected term (in years)		8.2 - 10.0				9.2 - 10.0
Expected volatility		91.3% - 94.9%				77.9% - 78.1%
Risk-free interest rate		2.4% - 2.6%				2.7% - 2.8%
Expected dividend yield		0.0%				0.0%

Summary of Restricted Stock Activity

The summary of restricted stock activity and related information follows:

		Number of Restricted Shares Outstanding
Unvested shares — December 31, 2018			1,000
Vested			(500	)
Unvested shares — March 31, 2019			500

Summary of Restricted Stock Units Activity

The summary of restricted stock unit activity and related information follows:

		Number of Restricted Stock Units Outstanding
Unvested shares — December 31, 2018			24,960
Granted			—
Vested			—
Unvested shares — March 31, 2019			24,960

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