Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of Share-based Compensation, Stock Options, Activity

A summary of the Company’s stock option activity under the 2012 Stock Plan (as amended and restated, the “2012 Plan”) and the 2018 Incentive Award Plan (the “2018 Plan”) and related information is as follows:

			Options Outstanding
	Shares Available for Grant		Shares Subject to Options Outstanding		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life (Years)	Aggregate Intrinsic Value
								(in thousands)
Balance as of December 31, 2019	2,726,225		4,494,889		$	10.90	7.7	$	306,392
2018 plan annual increase(1)	3,689,000		—
Granted	(6,902	)	6,902		84.61
Exercised	—		(242,003	)	6.21
Canceled	12,406		(31,798	)	10.90
Restricted stock units granted	(14,548	)	—		—
Restricted stock units canceled	16,164		—		—
Balance as of March 31, 2020	6,422,345		4,227,990		$	11.29	7.5	$	253,161
Vested and Exercisable as of March 31, 2020			2,034,629		$	5.77	7.1	$	130,646

(1)

Effective as of January 1, 2020, an additional 3,689,000 shares of common stock became available for issuance under the 2018 Plan, as a result of the operation of an automatic annual increase provision therein.

Schedule of Restricted Stock Activity

A summary of the Company’s restricted stock unit activity under the 2012 Plan and the 2018 Plan and related information is as follows:

	Restricted Stock Units Outstanding		Weighted-Average Grant Date Fair Value
Balance as of December 31, 2019	496,131		$	82.08
Granted	14,548		85.30
Vested	(5,594	)	67.81
Canceled	(16,164	)	71.97
Balance as of March 31, 2020	488,921		$	82.67

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

The following table presents the effect of employee and non‑employee related stock‑based compensation expense:

	Three Months Ended March 31,
	2020		2019
	(unaudited)
	(in thousands)
Cost of precision oncology testing	$	303	$	170
Research and development expense	2,364		1,210
Sales and marketing expense	1,798		826
General and administrative expense	1,873		976
Total stock-based compensation expense	$	6,338	$	3,182

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions

The grant date fair value of stock options was estimated using a Black-Scholes option-pricing model with the following weighted-average assumptions:

	Three Months Ended March 31,
	2020	2019
	(unaudited)
Expected term (in years)	6.06	6.22
Expected volatility	73.3%	66.7%
Risk-free interest rate	1.6%	2.7%
Expected dividend yield	—%	—%