Share-Based Payments (Tables)

3 Months Ended

Mar. 31, 2015

Summary of Stock Option Activity and Related Information

A summary of the Company’s stock option activity and related information follows:

	Shares			Weighted-Average Exercise Price		Remaining Contractual Life (in years)
Outstanding at December 31, 2014		1,438,528		$	4.93		7.86
Granted		566,556			10.78
Exercised		(54,371	)		0.82
Cancelled or forfeited		(17,555	)		6.83
Outstanding at March 31, 2015		1,933,158		$	6.74		8.27
Exercisable at March 31, 2015		645,757		$	3.91		7.35
Vested and expected to vest at March 31, 2015(1)		1,593,293		$	7.19		8.45

(1) Represents the number of vested options, plus the number of unvested options expected to vest.

Summary of Status and Changes of Unvested Restricted Stock

A summary of the status of unvested restricted stock is presented below:

	Restricted Stock			Weighted-Average Grant Date Fair Value
Unvested at December 31, 2014		125,027		$	5.39
Granted		1,300			10.08
Vested		(27,792	)		2.37
Unvested at March 31, 2015		98,535		$	6.31

Summary of Stock-based Compensation Expense

During the three months ended March 31, 2015 and 2014, the Company recorded stock-based compensation expense for employee and non-employee stock options and restricted stock, which was allocated as follows in the statements of operations (in thousands):

	Three Months Ended March 31,
	2015		2014
Research and development expense	$	280	$	355
General and administrative expense		384		281
	$	664	$	636

Employees and Directors Stock Option [Member]

Estimation of Fair Value of Stock Option Granted using Black-Scholes Option-Pricing Model Assumptions

The fair value of each stock option granted to employees and directors was estimated on the date of grant using the Black-Scholes option-pricing model based on the assumptions noted in the following table:

	Three Months Ended March 31,
	2015			2014
Risk-free interest rate		1.42–1.76	%		1.80-2.02	%
Expected dividend yield		—			—
Expected term (in years)		5.75-6			5.75-6
Expected volatility		73.07–74.11	%		69.37-69.58	%