Derek J. Maetzold, President and Chief Executive Officer of Castle Biosciences Inc., filed a Form 4 on September 1, 2026, disclosing stock option exercises and common stock sales executed on August 28, 2026, under a pre-established Rule 10b5-1 trading plan.

Key Highlights

  • Option exercise: Maetzold exercised a fully vested stock option covering 12,428 shares of common stock at an exercise price of $2.39 per share.
  • Direct share sales at weighted-average $33.14: 11,472 shares sold directly, with additional shares sold through multiple family trusts at the same weighted-average price, in trades ranging from $32.78 to $33.70.
  • Additional sales at weighted-average $33.88: Further shares sold directly and through family trusts at a weighted-average price of $33.88, in trades ranging from $33.78 to $33.97.
  • 10b5-1 plan: All transactions were made pursuant to a Rule 10b5-1 plan adopted by Maetzold on December 3, 2025.
  • Remaining direct ownership: Following all reported transactions, Maetzold directly held 21,479 shares of common stock.
  • Indirect holdings: Maetzold retains indirect beneficial ownership across multiple trusts, including 27,862 shares held by DJM Grantor Retained Annuity Trust No. 7 and 40,935 shares held by DJM Grantor Retained Annuity Trust No. 8.

Maetzold's August 28 Transactions: Option Exercise, Sales, and Trust Holdings at Castle Biosciences

According to the filing, Maetzold exercised a stock option for 12,428 shares of Castle Biosciences Inc. (NASDAQ:CSTL) common stock at an exercise price of $2.39 per share on August 28, 2026. The filing notes the shares subject to the option were fully vested. Following the exercise, Maetzold directly owned 33,907 shares before the reported sales were executed.

The filing discloses that Maetzold then sold shares both directly and through several family trusts. Direct sales totaled 11,472 shares at a weighted-average price of $33.14 and 956 shares at a weighted-average price of $33.88. Sales attributed to indirect holdings included shares disposed of through The Maetzold Descendants 2020 Trust, the Derek Maetzold 2020 Irrevocable Trust, and four separate Maetzold 2018 Remainder Trusts, each benefiting one of Maetzold's children. The filing states that the $33.14 transactions were executed in multiple trades at prices ranging from $32.78 to $33.70, inclusive, and the $33.88 transactions ranged from $33.78 to $33.97, inclusive. The filing notes Maetzold undertakes to provide full per-trade detail upon request.

The filing also discloses that Maetzold retains indirect beneficial ownership in shares held by DJM Grantor Retained Annuity Trust No. 6 (11,963 shares), No. 7 (27,862 shares), No. 8 (40,935 shares), and No. 9 (23,216 shares), in each of which he serves as trustee. Additionally, the filing shows 25,329 stock options (right to buy) beneficially owned directly following the reported transactions, with an exercise price of $2.39 and an expiration date of May 9, 2028.

What Was Disclosed

The filing reports a stock option exercise covering 12,428 shares and multiple sales of common stock executed on August 28, 2026, both directly and through family trusts, all under a Rule 10b5-1 plan adopted on December 3, 2025.