Castle Biosciences (CSTL) CEO sells 44,125 shares under 10b5-1 plan

Rhea-AI Filing Summary

Castle Biosciences President and CEO Derek J. Maetzold reported a pre-planned combination of option exercise and share sales. On March 11, 2026, he exercised a fully vested stock option for 6,226 shares of common stock at $2.39 per share and received the underlying shares.

That same day, Maetzold and several family-related trusts sold multiple blocks of common stock in open-market transactions at a weighted-average price of about $26.11. On March 12, 2026, he sold an additional 23,179 shares at an average price of $25.279 per share. All sales were made pursuant to a Rule 10b5-1 trading plan adopted on December 3, 2025. After these trades, he holds 71,558 shares directly, plus additional indirect holdings through various trusts.

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).

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 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)
03/11/2026

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	03/11/2026		M(1)		6,226	A	$2.39	112,047	D
Common Stock	03/11/2026		S(1)		17,310	D	$26.109(2)	94,737	D
Common Stock	03/11/2026		S(1)		1,357	D	$26.109(2)	51,566	I	By The Maetzold Descendants 2020 Trust(3)
Common Stock	03/11/2026		S(1)		1,160	D	$26.109(2)	43,826	I	By Derek Maetzold 2020 Irrevocable Trust(4)
Common Stock	03/11/2026		S(1)		282	D	$26.109(2)	3,336	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk(5)
Common Stock	03/11/2026		S(1)		279	D	$26.109(2)	3,336	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold(6)
Common Stock	03/11/2026		S(1)		279	D	$26.109(2)	3,336	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold(7)
Common Stock	03/11/2026		S(1)		279	D	$26.109(2)	3,336	I	By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold(8)
Common Stock	03/12/2026		S(1)		23,179	D	$25.279(9)	71,558	D
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
Stock option (right to buy)	$2.39	03/11/2026		M(1)			6,226	(13)	11/11/2028	Common Stock	6,226	$0	14,282	D

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 $25.800 to $26.630, 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. This transaction was executed in multiple trades at prices ranging from $24.900 to $25.705, 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.

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.

13. The shares subject to the option are fully vested.

Remarks:

	/s/ Frank Stokes, Attorney-in-fact	03/13/2026
	** 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.

FAQ

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

Derek Maetzold reported exercising a fully vested stock option for 6,226 Castle Biosciences shares and selling 44,125 shares in open-market trades. The activity includes both his direct holdings and shares held through various family-related trusts.

How many Castle Biosciences shares did the CEO sell in this filing?

The Form 4 shows total open-market sales of 44,125 Castle Biosciences common shares across March 11 and March 12, 2026. These include direct sales by Derek Maetzold and additional sales from multiple family trusts associated with him.

At what prices were CSTL shares sold in the reported transactions?

On March 11, 2026, Castle Biosciences shares were sold at a weighted-average price of about $26.109, with trades ranging from $25.800 to $26.630. On March 12, 2026, shares were sold at a weighted-average price of $25.279, with trades from $24.900 to $25.705.

Did the Castle Biosciences CEO exercise stock options in this Form 4?

Yes. Derek Maetzold exercised a fully vested stock option covering 6,226 Castle Biosciences shares at an exercise price of $2.39 per share on March 11, 2026. The exercised option converted into common stock that is reflected in his subsequent holdings.

Were the CSTL share sales by the CEO pre-planned under Rule 10b5-1?

Yes. The filing notes the transactions were made under a Rule 10b5-1 trading plan adopted on December 3, 2025. Such plans pre-schedule trades, indicating these sales were structured in advance rather than timed reactively to short-term market movements.

How many Castle Biosciences shares does Derek Maetzold hold after these trades?

Following the reported transactions, Derek Maetzold holds 71,558 Castle Biosciences shares directly. The Form 4 also lists substantial additional indirect holdings through several trusts where he or his family members are trustees, beneficiaries, or both.

Which trusts associated with the CSTL CEO are involved in these share sales?

Sales involve The Maetzold Descendants 2020 Trust, the Derek Maetzold 2020 Irrevocable Trust, and several Maetzold 2018 remainder trusts for individual family members. Additional indirect holdings are reported in DJM Grantor Retained Annuity Trusts Nos. 5, 6, and 7.