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Note 12 - Stock-based Compensation

6 Months Ended

Jun. 30, 2025

Notes to Financial Statements

Share-Based Payment Arrangement [Text Block]

Note 12—Stock-Based Compensation

Our stock option plans provide for the grant of incentive and non-qualified stock options, restricted stock awards, restricted stock units, and other stock awards to employees, non-employee directors, and consultants.

Stock-based compensation is as follows:

		Three Months Ended								Six Months Ended
		June 30,								June 30,
		2025				2024				2025				2024
		(In thousands)

Research and development		$	915			$	1,069			$	1,951			$	2,083
Selling, general and administrative			1,150				1,699				2,567				3,343
Total stock-based compensation		$	2,065			$	2,768			$	4,518			$	5,426

The fair value of each option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The following assumptions were applied to all stock option grants:

		Three Months Ended				Six Months Ended
		June 30, 2025				June 30, 2025
Estimated weighted-average fair value		$	2.57			$	2.61
Weighted-average assumptions:
Expected volatility			101	%			101	%
Expected life, in years			7.3				7.3
Risk-free interest rate			4.13	%			4.13	%
Expected dividend yield			—	%			—	%

Expected volatility is based on the historical volatility of our stock price weighted by grant issuances over the reporting period. We estimated the expected life of the stock options granted using the historical exercise behavior of option holders. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant. Forfeiture expense is estimated at the time of grant and revised in subsequent periods if actual forfeitures differ from those estimates.

Stock option activity for all stock plans and related information is as follows:

						Weighted-
						Average								Aggregate
						Exercise				Remaining				Intrinsic
		Options				Price per				Contractual Life				Value
		Outstanding				Share				(In years)				(In thousands)
Balance at December 31, 2024			16,690,882			$	8.17
Granted			3,296,700				3.29
Exercised			(26,702	)			3.30
Forfeited			(245,766	)			14.20
Balance at June 30, 2025			19,715,114			$	7.28				6.4			$	558
Vested and expected to vest at June 30, 2025			18,974,796			$	7.44				6.3			$	534
Exercisable at June 30, 2025			12,469,143			$	9.63				4.9			$	288

On June 30, 2025, annual stock options grants of approximately 3.1 million shares of common stock were awarded to eligible participants for the 2024 annual performance period under the 2017 Omnibus Incentive Compensation Plan.

Of the 19.7 million common stock options outstanding as of June 30, 2025, 16.9 million shares have an exercise price per share above $3.00, which was the closing price of our stock on the Nasdaq exchange on June 30, 2025.

As of June 30, 2025, there were 7.2 million unvested options outstanding that will vest over a weighted-average period of 2.8 years. The total estimated compensation expense yet to be recognized on outstanding options is $16.2 million.

As of June 30, 2025, the total number of shares of common stock available for grant was 3.8 million.