X0202 SCHEDULE 13G/A 0001493215-26-000032 0001493215 XXXXXXXX LIVE 1 Common Stock, $0.001 par value 03/31/2026 0001447362 Castle Biosciences, Inc. 14843C105 1500 W. Parkwood Ave., Suite 400 Friendswood TX 77546 Rule 13d-1(b) RTW Investments, LP DE 0.00 2758335.00 0.00 2758335.00 2758335.00 9.3 IA PN Roderick Wong X1 0.00 2758335.00 0.00 2758335.00 2758335.00 9.3 HC IN Castle Biosciences, Inc. 1500 W. Parkwood Ave., Suite 400, Friendswood, TX, 77546. This statement is filed by: (i) RTW Investments, LP ("RTW Investments"), a Delaware limited partnership and the investment adviser to certain funds (the "RTW Funds"), with respect to shares of Common Stock, par value $0.001 per share (the "Shares") of Castle Biosciences, Inc. (the "Company") directly held by the RTW Funds; and (ii) Roderick Wong, M.D. ("Dr. Wong"), the Managing Partner and Chief Investment Officer of RTW Investments, with respect to the Shares directly held by the RTW Funds. The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons." The filing of this statement should not be construed as an admission that any of the foregoing persons or any Reporting Person is, for the purposes of Section 13 of the Securities Exchange Act of 1934, as amended, the beneficial owner of the Shares reported herein. The address of the business office of each of the Reporting Persons is 40 10th Avenue, Floor 7, New York, New York 10014. RTW Investments is a Delaware limited partnership. Dr. Wong is a citizen of the United States. N IA HC The information required by Item 4(a) is set forth in Rows 5 - 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentages set forth in Row 11 of the cover pages are calculated based upon 29,731,198 Shares outstanding as of February 19, 2026 as reported in the Company's Annual Report on Form 10-K filed with the Securities and Exchange Commission on February 26, 2026. RTW Investments: 9.3% Dr. Wong: 9.3% RTW Investments: 0 Dr. Wong: 0 RTW Investments: 2,758,335 Shares Dr. Wong: 2,758,335 Shares RTW Investments: 0 Dr. Wong: 0 RTW Investments: 2,758,335 Shares Dr. Wong: 2,758,335 Shares Y N See Item 2. The RTW Funds have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares reported herein. Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. Exhibit 99.1 Joint Filing Agreement (incorporated by reference to Exhibit 99.1 to the Reporting Persons' Schedule 13G filed with the SEC on February 17, 2026). RTW Investments, LP /s/ Roderick Wong, M.D. 05/15/2026 Roderick Wong s/ Roderick Wong, M.D. 05/15/2026