Castle Biosciences (CSTL) CEO sells 19,300 shares under 10b5-1 plan

Rhea-AI Filing Summary

Castle Biosciences CEO Derek J. Maetzold reported open-market sales of 19,300 shares of Common Stock of CASTLE BIOSCIENCES INC. He sold 18,650 shares at a weighted-average price of $25.93 on March 17, 2026 and 650 shares at $25.39 on March 18, 2026, leaving 21,479 shares held directly.

The filing notes these transactions were executed under a pre-arranged Rule 10b5-1 trading plan adopted on December 3, 2025. Maetzold also reports indirect ownership of additional Common Stock through multiple family and grantor retained annuity trusts, including 51,566 shares held by The Maetzold Descendants 2020 Trust and other trusts where he serves as trustee or beneficiary.

SEC Form 4

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

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

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

MAETZOLD DEREK J

(Last) (First) (Middle)

C/O CASTLE BIOSCIENCES, INC.

1500 W. PARKWOOD AVE SUITE 400

(Street)

FRIENDSWOOD TEXAS 77546

(City) (State) (Zip)

UNITED STATES

(Country)

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
03/17/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	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	03/17/2026		S(1)		18,650	D	$25.93(2)	22,129	D
Common Stock	03/18/2026		S(1)		650	D	$25.39(3)	21,479	D
Common Stock								51,566	I	By The Maetzold Descendants 2020 Trust(4)
Common Stock								43,826	I	By Derek Maetzold 2020 Irrevocable Trust(5)
Common Stock								3,336	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk(6)
Common Stock								3,336	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold(7)
Common Stock								3,336	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold(8)
Common Stock								3,336	I	By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold(9)
Common Stock								85,959	I	By DJM Grantor Retained Annuity Trust No. 5(10)
Common Stock								18,718	I	By DJM Grantor Retained Annuity Trust No. 6(11)
Common Stock								44,323	I	By DJM Grantor Retained Annuity Trust No. 7(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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (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: 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

Explanation of Responses:

1. These transactions were made pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on December 3, 2025.

2. This transaction was executed in multiple trades at prices ranging from $25.66 to $26.27, inclusive. The price reported above reflects the weighted-average sale price. The Reporting Person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

3. This transaction was executed in multiple trades at prices ranging from $25.26 to $25.48, inclusive. The price reported above reflects the weighted-average sale price. The Reporting Person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

4. 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.

5. Held by Derek Maetzold 2020 Irrevocable Trust of which the Reporting Person is the trustee and his children are beneficiaries.

6. 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.

7. 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.

8. 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.

9. 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.

10. Held by DJM Grantor Retained Annuity Trust No. 5 of which the Reporting Person is the trustee and beneficiary.

11. Held by DJM Grantor Retained Annuity Trust No. 6 of which the Reporting Person is the trustee and the beneficiaries are The Maetzold 2018 Remainder Trust FBO John Derek Maetzold, The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk, The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold and The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold.

12. Held by DJM Grantor Retained Annuity Trust No. 7 of which the Reporting Person is the trustee and beneficiary.

Remarks:

	/s/ Frank Stokes, Attorney-in-fact	03/19/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)

FAQ

What did CSTL CEO Derek Maetzold report in this Form 4 filing?

The Form 4 shows CEO Derek Maetzold sold 19,300 Castle Biosciences shares in open-market transactions under a Rule 10b5-1 plan, at weighted-average prices around $26, and now holds 21,479 shares directly plus additional indirect holdings through several family-related trusts.

How many Castle Biosciences (CSTL) shares did the CEO sell and at what prices?

Derek Maetzold sold 18,650 CSTL shares at a weighted-average price of $25.93 on March 17, 2026 and 650 shares at $25.39 on March 18, 2026, totaling 19,300 shares sold in these reported open-market transactions.

Was the CSTL CEO’s stock sale done under a Rule 10b5-1 trading plan?

Yes. The filing states the transactions were made pursuant to a Rule 10b5-1 plan adopted by Derek Maetzold on December 3, 2025. Such pre-arranged plans automate trading and can indicate the timing was predetermined rather than based on short-term market developments.

How many Castle Biosciences shares does the CEO hold directly after these sales?

After the reported sales, Derek Maetzold directly holds 21,479 shares of Castle Biosciences Common Stock. This figure comes from the post-transaction holdings reported for the March 18, 2026 transaction, which lists the total shares beneficially owned in his direct account.

What indirect CSTL shareholdings are reported for Derek Maetzold in this filing?

The filing lists indirect ownership of Common Stock through several trusts, including 51,566 shares in The Maetzold Descendants 2020 Trust and additional shares in the Derek Maetzold 2020 Irrevocable Trust, multiple 2018 remainder trusts for family members, and DJM Grantor Retained Annuity Trusts Nos. 5, 6 and 7.

Are the CSTL CEO’s reported transactions open-market sales or other types of transfers?

The two transactions with share amounts are coded “S” and described as open-market or private sales of Common Stock. Other entries in the filing reflect holding balances in various trusts, with no share amounts transacted and no buy or sell direction indicated for those records.