Note 10 - Stock-based Compensation

12 Months Ended

Dec. 31, 2025

Notes to Financial Statements

Share-Based Payment Arrangement [Text Block]

10. Stock-Based Compensation

The Company recorded total stock-based compensation expense for stock options, stock awards and the Amended ESPP as follows (in thousands):

		Year Ended December 31,
		2025				2024
Research and development		$	246			$	375
Selling, general and administrative			453				614
Total		$	699			$	989

In the year ended December 31, 2025, there were 53,066 shares issued under the Amended ESPP. The weighted average fair value of shares issued under the Amended ESPP in 2025 and 2024 was $0.47 and $0.88 per share, respectively. As of December 31, 2025, there were 212,831 shares available for future grant under the Amended ESPP.

The following table summarizes restricted stock unit activity under the Company’s Equity Incentive Plans:

						Weighted
		Number of				Average
		Restricted				Grant Date
		Stock Units				Fair Value
Restricted stock units outstanding, January 1, 2024			86,232			$	7.57
Granted			176,768				1.03
Vested			(42,525	)			11.31
Forfeited			(7,552	)			2.03
Restricted stock units outstanding, December 31, 2024			212,923			$	1.59
Granted			158,966				0.69
Vested			(93,606	)			2.18
Forfeited			(5,088	)			0.80
Restricted stock units outstanding, December 31, 2025			273,195			$	0.88

The following table summarizes stock option activity under the Company’s Equity Incentive Plans:

		Number of Stock Options Outstanding				Weighted- Average Exercise Price				Weighted- Average Remaining Contractual Life (Years)				Aggregate Intrinsic Value
														(in thousands)
January 1, 2024			893,321			$	33.41
Granted			1,053,612				1.03
Forfeited			(41,156	)			1.75
Expired			(118,877	)			71.96
January 1, 2025			1,786,900			$	12.48
Granted			919,781				0.70
Exercised			(14,000	)			1.03
Forfeited			(32,561	)			0.93
Expired			(49,643	)			49.11
December 31, 2025			2,610,477			$	7.84				7.6			$	519

Vested and exercisable options—December 31, 2025			1,122,077			$	17.06				6.0			$	72
Vested and expected to vest—December 31, 2025			2,610,477			$	7.84				7.6			$	519

As of December 31, 2025, there were 1,954,964 shares available for future grant under the 2020 EIP.

Additional information regarding the Company’s stock options outstanding and vested and exercisable as of December 31, 2025, is summarized below:

		Options Outstanding												Options Vested and Exercisable
Exercise Prices		Number of Stock Options Outstanding				Weighted-Average Remaining Contractual Life (Years)				Weighted-Average Exercise Price per Share				Shares Subject to Stock Options				Weighted-Average Exercise Price per Share
$0.58 - $0.89			812,073				9.1			$	0.62				102,673			$	0.84
$0.91 - $1.37			1,104,289				8.5			$	1.06				399,937			$	1.04
$1.76 - $2.64			244,272				7.1			$	1.76				173,021			$	1.76
$4.62 - $6.93			10,850				6.5			$	4.62				10,850			$	4.62
$8.03 - $12.05			82,079				6.1			$	8.07				78,682			$	8.07
$14.40 - $21.60			9,083				4.3			$	16.40				9,083			$	16.40
$22.40 - $33.60			11,700				5.1			$	28.62				11,700			$	28.62
$34,40 - $51.60			192,319				3.1			$	41.80				192,319			$	41.80
$57.40 - $86.10			143,812				0.9			$	63.48				143,812			$	63.48
			2,610,477				7.6			$	7.84				1,122,077			$	17.06

The weighted average grant-date fair value of options granted during the years ended December 31, 2025 and 2024, was $0.56 and $0.84 per share, respectively. As of December 31, 2025, total stock-based compensation expense related to unvested options to be recognized in future periods was $1.0 million which is expected to be recognized over a weighted-average period of 2.2 years. The grant date fair value of options vested during the years ended December 31, 2025 and 2024, was $0.7 million and $2.0 million, respectively. The total intrinsic value of options exercised during the year ended December 31, 2025 was de minimus. There were no options exercised during the year ended December 31, 2024. In addition, the performance-based stock options granted in March 2021 to certain of the Company’s executive officers remained unvested and expired during the year ended December 31, 2024.

The Company used the following assumptions to calculate the fair value of each time-based stock option:

	Year Ended December 31,
	2025		2024
Expected term (in years)	6.7		6.5
Risk-free interest rate	3.8% - 4.0%		4.1% - 4.5%
Expected volatility	95%		98%
Expected dividend rate	0%		0%