12. Stock-Based Compensation

Stock-based Compensation Expense

The following table presents stock-based compensation expense as reflected in the Company's consolidated statements of operations (in thousands):

 

 

Twelve Months Ended December 31,

 

 

 

2024

 

 

2023

 

Research and development

 

$

10,714

 

 

$

9,143

 

General and administrative

 

 

11,519

 

 

 

11,116

 

Total stock-based compensation

 

$

22,233

 

 

$

20,259

 

The following table presents stock-based compensation expense by type of award (in thousands):

 

 

Year Ended December 31,

 

 

 

2024

 

 

2023

 

Stock options

 

$

20,608

 

 

$

18,060

 

Restricted stock units

 

 

1,470

 

 

 

2,023

 

Employee Stock Purchase Plan

 

 

155

 

 

 

176

 

Total

 

$

22,233

 

 

$

20,259

 

Stock Options

A summary of stock option activity for the year ended December 31, 2024 is set forth below (in thousands, except share and per share data):

 

 

Number of
Shares
Underlying
Outstanding
Options

 

 

Weighted
Average
Exercise
Price

 

 

Weighted-
Average
Remaining
Contractual
Term
(in years)

 

 

Aggregate
Intrinsic
Value
(in thousands)

 

Outstanding, December 31, 2023

 

 

9,383,105

 

 

$

10.64

 

 

 

8.2

 

 

$

45

 

Options granted

 

 

7,549,053

 

 

$

2.47

 

 

 

 

 

 

 

Options exercised

 

 

(92,283

)

 

$

2.12

 

 

 

 

 

 

 

Options forfeited or cancelled

 

 

(1,874,605

)

 

$

7.60

 

 

 

 

 

 

 

Outstanding, December 31, 2024

 

 

14,965,270

 

 

$

3.09

 

 

 

8.1

 

 

$

 

Options exercisable, December 31, 2024

 

 

7,327,757

 

 

$

3.41

 

 

 

7.4

 

 

$

 

Vested and expected to vest, December 31, 2024

 

 

14,965,270

 

 

$

3.09

 

 

 

8.1

 

 

$

 

The assumptions used in the Black Scholes Model to calculate stock-based compensation are as follows:

 

 

Twelve Months Ended December 31,

 

 

2024

 

2023

Fair value of common stock

 

$0.96 - $3.12

 

$1.32 - $9.15

Expected term (years)

 

5.5 - 6.08

 

5.5 - 6.1

Volatility

 

82.15% - 88.46%

 

83.25% - 92.87%

Risk free rates

 

3.63% - 4.52%

 

3.5% - 4.86%

Dividend rate

 

0.0%

 

0.0%

 

The fair value of each stock option was estimated at the date of grant using a Black-Scholes option-pricing model using the following assumptions:

The assumptions are as follows:

Expected volatility. The Company has limited trading history. As such, the expected volatility was determined by examining the historical volatilities for comparable publicly traded companies within the biotechnology and pharmaceutical industry using an average of historical volatilities of the Company’s industry peers.
Risk-free interest rate. The risk-free interest rate is based on the United States Treasury yield with a maturity equal to the expected term of the option in effect at the time of grant.
Dividend yield. The expected dividend is assumed to be zero as dividends have never been paid and there are no current plans to pay dividends on common stock.
Expected term. The expected term represents the period that the stock-based awards are expected to be outstanding. The expected term is calculated using the simplified method which is used when there is insufficient historical data about exercise patterns and post-vesting employment termination behavior. The simplified method is based on the vesting period and the contractual term for each grant, or for each vesting-tranche for awards with graded vesting. The mid-point between the vesting date and the maximum contractual expiration date is used as the expected term under this method. For awards with multiple vesting-tranches, the times from grant until the mid-points for each of the tranches may be averaged to provide an overall expected term.

The Company will continue to use judgment in evaluating the expected volatility, risk-free interest rates, dividend yield and expected term, utilized for stock-based compensation on a prospective basis.

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the fair value of the Company’s common stock for stock options that were in-the-money at December 31, 2024 and 2023. The aggregate intrinsic value of stock options exercised was less than $0.1 million during the years ended December 31, 2024 and 2023.

The total fair value of options that vested during the years ended December 31, 2024 and 2023 was $18.0 million and $17.9 million, respectively. The options granted during the years ended December 31, 2024 and 2023 had a weighted-average per share grant-date fair value of $1.40 per share and $3.94 per share, respectively.

As of December 31, 2024, the total unrecognized stock-based compensation expense related to unvested stock options was $18.6 million, which is expected to be recognized over the remaining weighted-average vesting period of 2.3 years.

In August 2024, certain of our executive officers entered into an option cancellation agreement to surrender certain underwater stock options. This voluntary surrender of stock options was determined to be a settlement for no consideration and the remaining unrecognized compensation cost was recognized immediately upon cancellation. This resulted in $1.6 million of stock-based compensation recognized in the third quarter of 2024 for these options.

Restricted Stock Units

The summary of RSU activity and related information for the year ended December 31, 2024 is set forth below:

 

 

Number of Units Outstanding

 

 

Weighted Average
Grant Date Fair Value

 

Outstanding, December 31, 2023

 

 

454,200

 

 

$

7.69

 

RSUs granted

 

 

537,400

 

 

$

2.60

 

RSUs vested

 

 

(184,380

)

 

$

7.15

 

RSUs forfeited

 

 

(87,564

)

 

$

4.21

 

Outstanding, December 31, 2024

 

 

719,656

 

 

$

4.40

 

 

The Company granted 537,400 and 513,700 RSU's in the years ended December 31, 2024 and 2023, respectively. The weighted-average grant date fair value of RSUs granted during the years ended December 31, 2024 and 2023 was $2.60 and $7.47, respectively.

As of December 31, 2024, there was approximately $1.9 million of unrecognized compensation cost related to unvested RSUs that the Company expects to recognize over a remaining weighted-average period of approximately 1.6 years.

Option repricing

On August 8, 2023, the board of directors approved a stock option repricing (the Option Repricing) effective on August 14, 2023 (the Effective Date) in accordance with the terms of the Company’s 2015 Stock Incentive Plan (the 2015 Plan) and Second Amended and Restated 2018 Stock Option and Incentive Plan (the 2018 Plan, and together with the 2015 Plan, the Plans). Pursuant to the Option Repricing, the exercise price of each stock option previously granted under the Plans, totaling 6,431,910 options, was amended to reduce the exercise price of such options to $2.14 per share, the closing price of the Company’s common stock on the Nasdaq Global Market on the Effective Date.

The repriced options otherwise retained their existing terms and conditions as set forth in the Plans and applicable award agreements. The stock option modification resulted in $4.6 million of incremental compensation cost, which was calculated using the Black-Scholes option-pricing model. Of the incremental compensation cost, $2.3 million and $1.3 million was recognized in the twelve months ended December 31, 2024 and 2023, respectively. The remaining incremental compensation cost of $0.6 million, net of the reversal of expense related to employee terminations prior to August 14, 2024, will be recognized on the straight-line basis over the remaining vesting period of the repriced options. The incremental cost is included in general and administrative expense and research and development expense on the consolidated statements of operations.

Effective August 21, 2024, the board of directors approved a rescission of the Option Repricing for certain non-employee directors of the Company. All of the affected stock options have been reverted to their original exercise price as established at the time of the grant. The Company will continue to recognize the incremental fair value from the Option Repricing for the impacted options. The compensation expense associated with the Option Repricing for these options was not material.

About Stock Compensation Disclosures

Stock-based compensation disclosures detail the equity awards granted to employees and executives — including stock options, restricted stock units (RSUs), and performance shares — along with the valuation methods and assumptions used to expense them. This section reveals the true cost of talent retention and the alignment between management incentives and shareholder interests.

Key signals: total unrecognized compensation expense and its expected recognition period signal future earnings headwinds from already-granted awards. For stock options, examine Black-Scholes assumptions — expected volatility, risk-free rate, and expected term — as understating any of these reduces reported compensation expense. Compare stock compensation expense as a percentage of revenue against peers to assess dilution cost. Watch vesting schedules for acceleration clauses tied to change-of-control events. Performance-based awards with undemanding targets may indicate weak governance. Add back stock compensation to operating cash flow to calculate a more conservative free cash flow figure.