Portolan Capital Management Reports 4.45% Stake in Castle Biosciences, Inc. (CSTL)

Portolan Capital Management, LLC, along with its manager George McCabe, filed a Schedule 13G/A on May 15, 2026, disclosing a significant position in Castle Biosciences, Inc. (CSTL). As of the event date on March 31, 2026, the reporting persons beneficially own 1,350,283 shares of Common Stock, representing 4.45% of the class. This filing serves as an amendment (Amendment No. 1) to a previous submission. Portolan Capital Management, LLC serves as the investment manager for various clients, while George McCabe holds indirect ownership as the Manager of the firm. Both reporting persons exercise sole voting and dispositive power over the reported shares. Notably, the filing indicates that the reporting persons have crossed below the 5% ownership threshold, as Item 5 is checked for the ownership of 5% or less of the class of securities. The securities were acquired in the ordinary course of business and not for the purpose of influencing or changing the control of the issuer.