Castle Biosciences CEO sells 8,580 shares

The transactions were made under a Rule 10b5-1 plan adopted June 2, 2026.

Rhea-AI Filing Summary

Castle Biosciences Inc. (CSTL) President and CEO Derek J. Maetzold exercised fully vested options for 8,580 common shares on September 21, 2026, at an exercise price of $2.39 per share, then sold those shares at a weighted-average $35.334 per share. The Maetzold Descendants 2020 Trust sold 3,198 shares and the Derek Maetzold 2020 Irrevocable Trust sold 2,718 shares, each at the same weighted-average price. The transactions were made under a Rule 10b5-1 plan adopted June 2, 2026.

Insider Trade Summary 10b5-1

Exercise and sale activity reported; no spread calculated

Exercise and Sale 13 txns

Insider MAETZOLD DEREK J

Role Pres. & Chief Exec. Officer

Sold 14,496 shs ($512K)

Approx. gross sale proceeds $512K

Approx. exercise cost $21K

Type	Security	Shares	Price	Value
Exercise	Stock option (right to buy) F1, F13	8,580	$0.00	$0.00
Exercise	Common Stock F1	8,580	$2.39	$21K
Sale	Common Stock F1, F2	8,580	$35.334	$303K
Sale	Common Stock F1, F2, F3	3,198	$35.334	$113K
Sale	Common Stock F1, F2, F4	2,718	$35.334	$96K
holding	Common Stock F5	--	--	--
holding	Common Stock F6	--	--	--
holding	Common Stock F7	--	--	--
holding	Common Stock F8	--	--	--
holding	Common Stock F9	--	--	--
holding	Common Stock F10	--	--	--
holding	Common Stock F11	--	--	--
holding	Common Stock F12	--	--	--

Holdings After Transaction: Stock option (right to buy) — 8,165 contracts (Direct); Common Stock — 21,479 shares (Direct); Common Stock — 11,236 shares (Indirect, By The Maetzold Descendants 2020 Trust); Common Stock — 9,550 shares (Indirect, By Derek Maetzold 2020 Irrevocable Trust); Common Stock — 11,256 shares (Indirect, By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk); Common Stock — 11,256 shares (Indirect, By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold); Common Stock — 11,256 shares (Indirect, By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold); Common Stock — 11,256 shares (Indirect, By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold); Common Stock — 11,963 shares (Indirect, By DJM Grantor Retained Annuity Trust No. 6); Common Stock — 27,862 shares (Indirect, By DJM Grantor Retained Annuity Trust No. 7); Common Stock — 40,935 shares (Indirect, By DJM Grantor Retained Annuity Trust No. 8); Common Stock — 23,216 shares (Indirect, DJM Grantor Retained Annuity Trust No. 9)

Footnotes (13)

1. F1. These transactions were made pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 2, 2026.
2. F2. This transaction was executed in multiple trades at prices ranging from $35.020 to $35.665, 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. F3. 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. F4. Held by Derek Maetzold 2020 Irrevocable Trust of which the Reporting Person is the trustee and his children are beneficiaries.
5. F5. 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. F6. 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. F7. 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. F8. 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. F9. 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. F10. Held by DJM Grantor Retained Annuity Trust No. 7 of which the Reporting Person is the trustee and beneficiary.
11. F11. Held by DJM Grantor Retained Annuity Trust No. 8 of which the Reporting Person is the trustee and beneficiary.
12. F12. Held by DJM Grantor Retained Annuity Trust No. 9 of which the Reporting Person is the trustee and beneficiary.
13. F13. The shares subject to the option are fully vested.

Key Figures

Options exercised: 8,580 options Exercise price: $2.39 per share Direct common-stock sale: 8,580 shares at weighted-average $35.334 per share +4 more

7 metrics

Options exercised 8,580 options Fully vested options exercised for common shares on September 21, 2026

Exercise price $2.39 per share Options exercised on September 21, 2026

Direct common-stock sale 8,580 shares at weighted-average $35.334 per share Derek J. Maetzold; September 21, 2026

Maetzold Descendants 2020 Trust sale 3,198 shares at weighted-average $35.334 per share September 21, 2026

Derek Maetzold 2020 Irrevocable Trust sale 2,718 shares at weighted-average $35.334 per share September 21, 2026

Options following exercise 8,165 options Reported after the exercise on September 21, 2026

Post-sale trust holdings 11,236 shares; 9,550 shares The Maetzold Descendants 2020 Trust; Derek Maetzold 2020 Irrevocable Trust, respectively

Key Terms

Rule 10b5-1 plan, weighted-average sale price, fully vested

3 terms

Rule 10b5-1 plan regulatory

"made pursuant to a Rule 10b5-1 plan adopted by the Reporting Person"

A Rule 10b5-1 plan is a prearranged, written schedule that lets corporate insiders buy or sell company stock at set times or amounts, even if they later learn material nonpublic information. Think of it like setting an automatic thermostat for trades: it creates a clear record that trades were planned in advance, reducing the risk of insider-trading accusations and helping investors trust that insider transactions are routine rather than based on secret information.

weighted-average sale price financial

"price reported above reflects the weighted-average sale price"

fully vested financial

"shares subject to the option are fully vested"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many CSTL shares did Derek J. Maetzold and the trusts sell?

Derek J. Maetzold sold 8,580 common shares at a weighted-average $35.334 per share; The Maetzold Descendants 2020 Trust sold 3,198 shares and the Derek Maetzold 2020 Irrevocable Trust sold 2,718 shares at the same weighted-average price. The sales occurred on September 21, 2026.

How many CSTL options did Derek J. Maetzold exercise, and at what price?

He exercised fully vested options for 8,580 common shares on September 21, 2026, at an exercise price of $2.39 per share. The option transaction reported 8,165 options following the exercise.

How many CSTL shares did the two trusts hold after their sales?

The Maetzold Descendants 2020 Trust held 11,236 shares after its sale, and the Derek Maetzold 2020 Irrevocable Trust held 9,550 shares after its sale. These are the separately reported post-sale holdings for the two trusts.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 09/23/2026 - 04:28 PM Accepted by SEC EDGAR 09/23/2026 - 04:27 PM Learn about SEC filing dates

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.

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)
09/21/2026

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	09/21/2026		M(1)		8,580	A	$2.39	30,059	D
Common Stock	09/21/2026		S(1)		8,580	D	$35.334(2)	21,479	D
Common Stock	09/21/2026		S(1)		3,198	D	$35.334(2)	11,236	I	By The Maetzold Descendants 2020 Trust(3)
Common Stock	09/21/2026		S(1)		2,718	D	$35.334(2)	9,550	I	By Derek Maetzold 2020 Irrevocable Trust(4)
Common Stock								11,256	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk(5)
Common Stock								11,256	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold(6)
Common Stock								11,256	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold(7)
Common Stock								11,256	I	By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold(8)
Common Stock								11,963	I	By DJM Grantor Retained Annuity Trust No. 6(9)
Common Stock								27,862	I	By DJM Grantor Retained Annuity Trust No. 7(10)
Common Stock								40,935	I	By DJM Grantor Retained Annuity Trust No. 8(11)
Common Stock								23,216	I	DJM Grantor Retained Annuity Trust No. 9(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	09/21/2026		M(1)			8,580	(13)	05/09/2028	Common Stock	8,580	$0	8,165	D

Explanation of Responses:

1. These transactions were made pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 2, 2026.

2. This transaction was executed in multiple trades at prices ranging from $35.020 to $35.665, 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. 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. Held by DJM Grantor Retained Annuity Trust No. 8 of which the Reporting Person is the trustee and beneficiary.

12. Held by DJM Grantor Retained Annuity Trust No. 9 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	09/23/2026
	** 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)