Castle Biosciences (CSTL) CEO executes 10b5-1 share sales, exercises options

Rhea-AI Filing Summary

Castle Biosciences (CSTL) President and CEO Derek J. Maetzold reported exercising stock options and selling shares in a pre-planned transaction. He exercised options for 550 shares of common stock at $2.39 per share, then sold a total of 4,172 common shares at a weighted-average price of $25.551 per share under a Rule 10b5-1 trading plan.

After these transactions, Maetzold holds 21,479 common shares directly and 13,732 options, with additional indirect holdings through several family trusts, including 50,209 shares in The Maetzold Descendants 2020 Trust and 42,673 shares in the Derek Maetzold 2020 Irrevocable Trust.

Insider Trade Summary 10b5-1

Net Seller: 4,172 shares ($106,599)

Net Sell 12 txns

Insider MAETZOLD DEREK J

Role Pres. & Chief Exec. Officer

Sold 4,172 shs ($107K)

Type	Security	Shares	Price	Value
Exercise	Stock option (right to buy)	550	$0.00	--
Exercise	Common Stock	550	$2.39	$1K
Sale	Common Stock	550	$25.551	$14K
Sale	Common Stock	1,357	$25.551	$35K
Sale	Common Stock	1,153	$25.551	$29K
Sale	Common Stock	278	$25.551	$7K
Sale	Common Stock	278	$25.551	$7K
Sale	Common Stock	278	$25.551	$7K
Sale	Common Stock	278	$25.551	$7K
holding	Common Stock	--	--	--
holding	Common Stock	--	--	--
holding	Common Stock	--	--	--

Holdings After Transaction: Stock option (right to buy) — 13,732 shares (Direct); Common Stock — 22,029 shares (Direct); Common Stock — 50,209 shares (Indirect, By The Maetzold Descendants 2020 Trust)

Footnotes (1)

1. These transactions were made pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on December 3, 2025. This transaction was executed in multiple trades at prices ranging from $25.050 to $25.955, 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. 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. Held by Derek Maetzold 2020 Irrevocable Trust of which the Reporting Person is the trustee and his children are beneficiaries. 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. 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. 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. 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. Held by DJM Grantor Retained Annuity Trust No. 5 of which the Reporting Person is the trustee and beneficiary. 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. Held by DJM Grantor Retained Annuity Trust No. 7 of which the Reporting Person is the trustee and beneficiary. The shares subject to the option are fully vested.

Key Figures

Options exercised: 550 shares at $2.39 Shares sold: 4,172 shares at $25.551 Direct common shares after: 21,479 shares +4 more

7 metrics

Options exercised 550 shares at $2.39 Stock option exercise into common stock

Shares sold 4,172 shares at $25.551 Weighted-average sale price for open-market sales

Direct common shares after 21,479 shares Direct CSTL holdings following transactions

Options remaining 13,732 options Stock options held after the 550-share exercise

Descendants 2020 Trust holding 50,209 shares Common shares held by The Maetzold Descendants 2020 Trust

Irrevocable Trust holding 42,673 shares Common shares held by Derek Maetzold 2020 Irrevocable Trust

DJM GRAT No. 5 holding 85,959 shares Common shares held by DJM Grantor Retained Annuity Trust No. 5

Key Terms

Rule 10b5-1 plan, stock option (right to buy), Grantor Retained Annuity Trust, weighted-average sale price, +1 more

5 terms

Rule 10b5-1 plan financial

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

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.

stock option (right to buy) financial

"security_title: Stock option (right to buy) ... conversion_or_exercise_price: 2.3900"

Grantor Retained Annuity Trust financial

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

A grantor retained annuity trust (GRAT) is an estate-planning tool where the person who creates the trust transfers assets into it but receives fixed cash payments (an annuity) from the trust for a set number of years; whatever remains after that term passes to designated beneficiaries. It matters to investors because it can shift future appreciation of assets out of the creator’s taxable estate—like putting an asset into a timed vending machine that pays you fixed amounts while any extra value that grows inside the machine goes to heirs with reduced gift or estate tax consequences.

weighted-average sale price financial

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

fully vested financial

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

Form 4 Insider Transactions: What Each Field Means →

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)
03/26/2026

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	03/26/2026		M(1)		550	A	$2.39	22,029	D
Common Stock	03/26/2026		S(1)		550	D	$25.551(2)	21,479	D
Common Stock	03/26/2026		S(1)		1,357	D	$25.551(2)	50,209	I	By The Maetzold Descendants 2020 Trust(3)
Common Stock	03/26/2026		S(1)		1,153	D	$25.551(2)	42,673	I	By Derek Maetzold 2020 Irrevocable Trust(4)
Common Stock	03/26/2026		S(1)		278	D	$25.551(2)	3,058	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk(5)
Common Stock	03/26/2026		S(1)		278	D	$25.551(2)	3,058	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold(6)
Common Stock	03/26/2026		S(1)		278	D	$25.551(2)	3,058	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold(7)
Common Stock	03/26/2026		S(1)		278	D	$25.551(2)	3,058	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
Stock option (right to buy)	$2.39	03/26/2026		M(1)			550	(12)	11/11/2028	Common Stock	550	$0	13,732	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 $25.050 to $25.955, 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.

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

Remarks:

	/s/ Frank Stokes, Attorney-in-fact	03/30/2026
	** 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 insider transactions did CSTL CEO Derek Maetzold report on this Form 4?

Derek Maetzold reported exercising options for 550 Castle Biosciences shares at $2.39 and selling 4,172 common shares at a weighted-average $25.551. The filing also updates his remaining direct and trust-held share positions following these transactions.

Were Derek Maetzold’s CSTL share sales made under a Rule 10b5-1 plan?

Yes. The filing states the transactions were made pursuant to a Rule 10b5-1 plan adopted on December 3, 2025. Such plans pre-schedule trades, indicating these sales were arranged in advance rather than timed discretionarily around short-term market movements.

How many Castle Biosciences shares does Derek Maetzold hold directly after the transactions?

After the reported trades, Derek Maetzold holds 21,479 Castle Biosciences common shares directly. He also retains 13,732 stock options and maintains significant additional indirect holdings through multiple family and grantor retained annuity trusts.

What price did Derek Maetzold receive for the CSTL shares he sold?

The reported sales were executed at a weighted-average price of $25.551 per share, with individual trades ranging from $25.050 to $25.955. The filing notes he can provide full trade details, including exact share amounts at each price, upon request.

What indirect Castle Biosciences holdings are associated with Derek Maetzold’s family trusts?

The filing lists several family trusts holding CSTL shares, including 50,209 shares in The Maetzold Descendants 2020 Trust and 42,673 shares in the Derek Maetzold 2020 Irrevocable Trust, plus multiple 2018 remainder trusts and three DJM Grantor Retained Annuity Trusts.

Did Derek Maetzold retain stock options in CSTL after this option exercise?

Yes. After exercising options for 550 shares at a $2.39 strike price, Derek Maetzold still holds 13,732 stock options. The filing indicates the option shares involved in this transaction were fully vested at the time of exercise.