Castle Biosciences (CSTL) insider details RSU vesting, tax trades

Rhea-AI Filing Summary

Castle Biosciences’ president, chief executive officer and director reported multiple stock transactions tied to restricted stock unit (RSU) vesting. On December 9, 2025, RSUs converted into 33,495 shares of common stock, followed by the disposition of 13,181 shares at $38.25 per share to cover tax obligations. On December 10, 2025, additional RSUs converted into 15,424 shares, with 6,070 shares disposed of at $38.02 per share for taxes, leaving 67,215 shares of common stock held directly.

The reporting person also lists indirect beneficial ownership in Castle Biosciences common stock through several family and grantor retained annuity trusts, each holding separate blocks of shares for the benefit of the reporting person, spouse and children.

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
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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).

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)
12/09/2025

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	12/09/2025		M		33,495	A	(1)	71,042	D
Common Stock	12/09/2025		F		13,181	D	$38.25	57,861	D
Common Stock	12/10/2025		M		15,424	A	(1)	73,285	D
Common Stock	12/10/2025		F		6,070	D	$38.02	67,215	D
Common Stock								52,923	I	By The Maetzold Descendants 2020 Trust(2)
Common Stock								44,986	I	By Derek Maetzold 2020 Irrevocable Trust(3)
Common Stock								3,618	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk(4)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold(5)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold(6)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold(7)
Common Stock								85,959	I	By DJM Grantor Retained Annuity Trust No. 5(8)
Common Stock								18,718	I	By DJM Grantor Retained Annuity Trust No. 6(9)
Common Stock								44,323	I	By DJM Grantor Retained Annuity Trust No. 7(10)

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
Restricted Stock Units	(1)	12/09/2025		M			33,495	(11)	(11)	Common Stock	33,495	$0	33,496	D
Restricted Stock Units	(1)	12/10/2025		M			15,424	(12)	(12)	Common Stock	15,424	$0	0	D

Explanation of Responses:

1. Each Restricted Stock Unit ("RSU") represents the right to receive one share of the Issuer's Common Stock.

2. 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.

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

4. 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.

5. 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.

6. 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.

7. 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.

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

9. 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.

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

11. On December 9, 2022, the Reporting Person was granted 133,983 RSUs which vest in four equal installments beginning on December 9, 2023.

12. On December 10, 2021, the Reporting Person was granted 61,698 RSUs which vest in four equal installments beginning on December 10, 2022.

Remarks:

	/s/ Frank Stokes, Attorney-in-fact	12/11/2025
	** 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 insider stock transactions did Castle Biosciences (CSTL) report on December 9, 2025?

The company’s president and CEO reported RSU-related transactions on December 9, 2025, with RSUs converting into 33,495 shares of common stock and 13,181 shares disposed of at $38.25 per share to cover taxes.

What insider transactions did Castle Biosciences (CSTL) report on December 10, 2025?

On December 10, 2025, additional RSUs converted into 15,424 shares of Castle Biosciences common stock, and 6,070 shares were disposed of at $38.02 per share for tax withholding.

How many Castle Biosciences shares does the reporting person hold directly after these transactions?

Following the reported RSU conversions and tax-related share dispositions, the reporting person directly holds 67,215 shares of Castle Biosciences common stock.

What types of equity awards are involved in this Castle Biosciences (CSTL) insider filing?

The filing involves restricted stock units (RSUs), each RSU representing the right to receive one share of Castle Biosciences common stock upon vesting, as stated in the explanations of responses.

Does the Castle Biosciences insider have indirect ownership through trusts?

Yes. The filing shows additional indirect beneficial ownership of Castle Biosciences common stock through multiple family and grantor retained annuity trusts, where the reporting person serves as trustee and/or beneficiary.

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

The reporting person is identified as both a director and an officer, with the title President & Chief Executive Officer of Castle Biosciences.