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Note 6 - Stockholders' Equity and Stock-based Compensation (Tables)
12 Months Ended
Dec. 31, 2024
Notes Tables  
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]
          

Weighted

 
          

Average

 
      

Weighted

  

Remaining

 
  

Number of

  

Average

  

Contractual

 
  

Shares

  

Exercise Price

  

Life (in Years)

 

Warrants outstanding at December 31, 2023

    $    

Issued

  5,999,999   11.00     

Exercised

  (4,501,516)  11.00     

Expired/Redeemed

          

Warrants outstanding at December 31, 2024

  1,498,483  $11.00   1.12 
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
  

Year Ended December 31,

 
  

2024

  

2023

 

Research and development

  6,293   3,491 

General and administrative

  7,293   3,690 

Total stock-based compensation expense

 $13,586  $7,181 
  

Year Ended December 31,

 
  

2024

  

2023

 

Time-based options

 $10,343  $3,827 

Performance-based options

  38   1,977 

Market-based options

  2,926   1,130 

ESPP

  279   247 

Total stock-based compensation expense

 $13,586  $7,181 
Market-based Options [Member]  
Notes Tables  
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
  

Stock Options Outstanding

 
  

Number of shares

  

Weighted average exercise price

  

Weighted average remaining life (in years)

 

Balances — December 31, 2023

  2,100,000  $6.78   9.44 

Options granted

  855,000   8.16     

Options exercised

          

Options canceled

  (700,000)  7.45     

Options expired

          

Options modified from performance-based to market-based

  206,389   5.39     

Balances — December 31, 2024

  2,461,389  $6.95   8.43 

Exercisable — December 31, 2024

         
Share-Based Payment Arrangement, Option [Member]  
Notes Tables  
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
  

Year Ended December 31,

 
  

2024

  

2023

 

Expected term in years

  

2.9 - 6.3

   

5.0 - 8.0

 

Expected volatility

  

91% - 99%

   

89% - 95%

 

Risk-free interest rate

  

3.8% - 4.5%

   

3.7% - 4.4%

 

Dividend yield

  

   

 
  

Year Ended December 31,

 
  

2024

  

2023

 

Expected term in years

  

1.4 - 4.3

   

4.0 - 6.3

 

Expected volatility

  

90%

   

90%

 

Risk-free interest rate

  

3.5% - 3.7%

   

3.4% - 3.8%

 

Dividend yield

  

   

 
Performance Options [Member]  
Notes Tables  
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
  

Stock Options Outstanding

 
  

Number of shares

  

Weighted average exercise price

  

Weighted average remaining life (in years)

 

Balances — December 31, 2023

  1,224,130  $5.51   8.53 

Options granted

  39,000   8.44     

Options exercised

  (9,950)  2.92     

Options canceled

  (3,000)  2.92     

Options expired

  (1,000)  2.92     

Options modified from performance-based to time-based and market-based

  (806,502)  4.49     

Balances — December 31, 2024

  442,678  $7.71   6.79 

Exercisable — December 31, 2024

  432,678  $7.69   6.73 
Time-based Options [Member]  
Notes Tables  
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
  

Stock Options Outstanding

 
  

Number of shares

  

Weighted average exercise price

  

Weighted average remaining life (in years)

 

Balances — December 31, 2023

  6,141,906  $10.48   7.07 

Options granted

  2,124,643   11.31     

Options exercised

  (150,897)  5.57     

Options canceled

  (605,542)  7.59     

Options expired

  (34,958)  20.30     

Options modified from performance-based to time-based

  600,113   4.18     

Balances — December 31, 2024

  8,075,265  $10.49   6.72 

Exercisable — December 31, 2024

  4,093,267  $13.27   4.80 
The 2017 Employee Stock Purchase Plan [Member]  
Notes Tables  
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
  

Year Ended December 31,

 
  

2024

  

2023

 

Expected term in years

  

0.5 - 1.0

   

0.5 - 1.0

 

Expected volatility

  

98%

   

83%

 

Risk-free interest rate

  

4.4% - 5.3%

   

5.1% - 5.5%

 

Dividend yield

  

   

 
The 2015 Plan, 2017 Plan and Inducement Plan [Member]  
Notes Tables  
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
  

Stock Options Outstanding

 
  

Number of shares

  

Weighted average exercise price

  

Weighted average remaining life (in years)

 

Balances — December 31, 2023

  9,466,036  $9.01   7.78 

Options granted

  3,018,643   10.38     

Options exercised

  (160,847)  5.41     

Options canceled

  (1,308,542)  7.51     

Options expired

  (35,958)  19.82     

Balances — December 31, 2024

  10,979,332  $9.59   7.11 

Exercisable — December 31, 2024

  4,525,945  $12.74   4.98