Sec Form 4 Filing - MAETZOLD DEREK J @ CASTLE BIOSCIENCES INC - 2022-04-26

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person MAETZOLD DEREK J 2. Issuer Name and Ticker or Trading Symbol CASTLE BIOSCIENCES INC [ CSTL] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Pres. & Chief Exec. Officer (Last) (First) (Middle) C/O CASTLE BIOSCIENCES, INC., 505 S. FRIENDSWOOD DRIVE, SUITE 401 3. Date of Earliest Transaction (MM/DD/YY) 04/26/2022 (Street) FRIENDSWOOD, TX77546 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 04/26/2022 A 22,311( 1 )( 2 ) A 201,934( 4 ) D Common Stock 55,603( 4 ) I By DJM Grantor Retained Annuity Trust No. 2( 5 ) Common Stock 75,000 I By DJM Grantor Retained Annuity Trust No. 3( 6 ) Common Stock 137,965 I By Derek Maetzold 2020 Irrevocable Trust( 7 ) Common Stock 150,567 I By The Maetzold Descendants 2020 Trust( 8 ) Common Stock 30,545 I By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold( 9 ) Common Stock 30,545 I By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold( 10 ) Common Stock 30,546 I By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk( 11 ) Common Stock 30,545 I By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold( 12 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MAETZOLD DEREK J C/O CASTLE BIOSCIENCES, INC. 505 S. FRIENDSWOOD DRIVE, SUITE 401 FRIENDSWOOD, TX77546 X Pres. & Chief Exec. Officer Signatures /s/ Greg Acosta, Attorney-in-fact 04/28/2022 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The reporting person acquired 22,311 shares of common stock on April 26, 2022, as consideration for the Reporting Person's equity securities of AltheaDx, Inc. ("AltheaDx"), which Castle Biosciences, Inc. ("Castle Biosciences") acquired by merger on April 26, 2022 (the "Merger") pursuant to an Agreement and Plan of Merger agreement dated April 4, 2022 (the "Merger Agreement"). Of the 22,311 shares issued to the Reporting Person in the Merger, 1,895 shares are currently being held in escrow and are subject to forfeiture for a specified period following the Merger to satisfy indemnification claims arising of Castle Biosciences, if any. ( 2 )The Merger Agreement provides that the former securityholders of AltheaDx may receive additional consideration, payable 50% in cash and 50% in shares of common stock of Castle Biosciences, based on the achievement of certain commercial milestones with related dates or performance periods through December 31, 2024 (the "Milestone Payments"). The portion of the Milestone Payments payable in shares of common stock will be valued at the volume-weighted average price for the 20 trading days ending as of the applicable determination date. The number of shares issuable is subject to certain limitations set forth in the Merger Agreement. The Reporting Person's right to receive additional shares pursuant to this earn-out right became fixed and irrevocable on April 26, 2022, the effective date of the merger. ( 3 )The number of shares issuable was determined pursuant to a formula set forth in the Merger Agreement, which provided that, for the purpose of determining the number of shares issuable, the shares of Castle Biosciences common stock would be valued at $42.54, which represents the volume weighted average share price of the stock for the 20 trading days immediately preceding the date of the Merger Agreement. ( 4 )On March 2, 2022, and March 3, 2022, the DJM Grantor Retained Annuity Trust No. 2 made annuity payments to the Reporting Person by transferring a total of 44,397 shares of Castle Biosciences, Inc. common stock to his direct holdings. ( 5 )Held by DJM Grantor Retained Annuity Trust No. 2 of which the Reporting Person is the trustee and beneficiary. ( 6 )Held by DJM Grantor Retained Annuity Trust No. 3 of which the Reporting Person is the trustee and beneficiary. ( 7 )Held by Derek Maetzold 2020 Irrevocable Trust of which the Reporting Person is the trustee and his children are beneficiaries. ( 8 )Held by The Maetzold Descendants 2020 Trust of which the Reporting Person's spouse is the trustee and the Reporting Person's spouse and their children are beneficiaries. ( 9 )Held by The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold of which the Reporting Person is the trustee and his child is the beneficiary. ( 10 )Held by The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold of which the Reporting Person is the trustee and his child is the beneficiary. ( 11 )Held by The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk of which the Reporting Person is the trustee and his child is the beneficiary. ( 12 )Held by The Maetzold 2018 Remainder Trust FBO John Derek Maetzold of which the Reporting Person is the trustee and his child is the beneficiary.

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