Castle Biosciences Insider Sale: 43,019 Shares by CEO Under 10b5-1 Plan

Rhea-AI Filing Summary

Derek J. Maetzold, President, CEO and Director of Castle Biosciences (CSTL), reported an insider sale under a Rule 10b5-1 plan. On 08/13/2025 he disposed of 43,019 shares of Castle common stock in multiple trades at a weighted-average sale price of $19.504 per share, reducing his direct holdings to 69,683 shares. The filing lists multiple indirect holdings across trusts (largest indirect positions: 85,959; 52,923; 44,986; 44,323; 18,718 shares) that remain held by various family and grantor retained annuity trusts. The 10b5-1 plan was adopted on November 11, 2024. The form is a routine Section 16 disclosure of an executed sale plan.

Positive

• Transaction executed under a documented Rule 10b5-1 plan, indicating pre-established trading authorization and regulatory compliance.

Negative

• Insider sale of 43,019 shares reduced direct ownership; while routine, it represents a net disposition by the CEO reported to the market.

Insights

Financial Analyst

TL;DR: Routine insider sale executed under a pre-established 10b5-1 plan; disclosure improves transparency but reduces direct share ownership.

The reported sale of 43,019 shares at a weighted-average price of $19.504 is explicitly identified as executed pursuant to a Rule 10b5-1 plan adopted on November 11, 2024. This is a common mechanism for officers to sell shares while mitigating insider-trading concerns. The filing shows the reporting person retains significant indirect and direct holdings across multiple trusts, indicating continued family exposure to the issuer. There is no additional financial or operational information in the filing to imply change in company fundamentals.

Corporate Governance Expert

TL;DR: Proper Section 16 disclosure and 10b5-1 plan invocation, demonstrating compliance with insider-trading procedures.

The Form 4 clearly identifies the reporter as Pres. & CEO and Director and documents the sale code (S) with explanatory footnotes describing the 10b5-1 plan and trust relationships. Signature by attorney-in-fact is provided. The disclosure shows governance procedures were followed: transactions were pre-planned and the registrant received standard notification. The filing contains no indications of deviations from required reporting protocols.

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

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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.

505 S. FRIENDSWOOD DRIVE, SUITE 401

(Street)

FRIENDSWOOD TX 77546

(City) (State) (Zip)

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

3. Date of Earliest Transaction (Month/Day/Year)
08/13/2025

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

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

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

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	08/13/2025		S(1)		43,019	D	$19.504(2)	69,683	D
Common Stock								52,923	I	By The Maetzold Descendants 2020 Trust(3)
Common Stock								44,986	I	By Derek Maetzold 2020 Irrevocable Trust(4)
Common Stock								3,618	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk(5)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold(6)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold(7)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold(8)
Common Stock								85,959	I	By DJM Grantor Retained Annuity Trust No. 5(9)
Common Stock								18,718	I	By DJM Grantor Retained Annuity Trust No. 6(10)
Common Stock								44,323	I	By DJM Grantor Retained Annuity Trust No. 7(11)

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, The Maetzold Descendants 2020 Trust, Derek Maetzold 2020 Irrevocable Trust, The Maetzold 2018 Remainder Trust f/b/o Emily Carol Kirk, The Maetzold 2018 Remainder Trust f/b/o Hannah Elizabeth Maetzold, The Maetzold 2018 Remainder Trust f/b/o John Derek Maetzold, and The Maetzold 2018 Remainder Trust f/b/o Peter Douglas Maetzold on November 11, 2024.

2. This transaction was executed in multiple trades at prices ranging from $19.265 to $19.880, 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. 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.

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

5. 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.

6. 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.

7. 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.

8. 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.

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

10. 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.

11. 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	08/15/2025
	** 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.

FAQ

What did Derek Maetzold report on Form 4 for CSTL?

He reported a sale of 43,019 shares of Castle Biosciences common stock on 08/13/2025 executed under a 10b5-1 plan.

At what price were the CSTL shares sold?

The sale was executed in multiple trades at prices ranging from $19.265 to $19.880, with a weighted-average sale price of $19.504 per share.

How many Castle shares does the reporting person own after the sale?

Following the reported transaction, the reporting person held 69,683 shares directly, plus various indirect trust holdings listed in the filing.

Was the sale part of a 10b5-1 plan and when was it adopted?

Yes. The transactions were made pursuant to a Rule 10b5-1 plan adopted on November 11, 2024, as stated in the filing.

What is the reporting person’s role at Castle Biosciences (CSTL)?

The reporting person, Derek J. Maetzold, is identified as President & Chief Executive Officer and a Director of Castle Biosciences.