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

Yes. The Form 4 states these CSTL share sales were made under a Rule 10b5-1 trading plan adopted on December 3, 2025. Such plans pre-schedule trades, meaning the timing of these transactions was set in advance rather than chosen opportunistically.

What were Derek Maetzold’s direct CSTL share holdings after these transactions?

After the reported trades, one direct account for Derek Maetzold shows 21,479 Castle Biosciences common shares. Additional indirect holdings are reported through various family and grantor retained annuity trusts, each with its own post-transaction share balance.

Castle Biosciences (CSTL) CEO reports planned stock sales and option exercises

Filing Impact

(Neutral)

Filing Sentiment

(Negative)

Form Type

Rhea-AI Filing Summary

CASTLE BIOSCIENCES INC President and CEO Derek J. Maetzold reported a series of insider trades in May 2026 involving company common stock. Across several family trusts and a personal account, entities associated with him sold a net 4,172 shares in open-market transactions at prices around $20 per share.

On the same dates, he exercised stock options to acquire 550 shares at an exercise price of $2.39 per share, increasing his direct common stock holdings. Following these transactions, one direct holding account shows 21,479 shares, while certain family trusts continue to hold tens of thousands of shares. The filing notes that these sales were executed under a pre-arranged Rule 10b5-1 trading plan adopted on December 3, 2025, indicating the trades were scheduled in advance rather than timed discretionarily.

Insider Trade Summary 10b5-1

Net Seller: 4,172 shares ($84,066)

Net Sell 21 txns

Insider MAETZOLD DEREK J

Role Pres. & Chief Exec. Officer

Sold 4,172 shs ($84K)

Type	Security	Shares	Price	Value
Exercise	Stock option (right to buy)	420	$0.00	--
Exercise	Common Stock	420	$2.39	$1K
Sale	Common Stock	420	$20.196	$8K
Sale	Common Stock	1,035	$20.196	$21K
Sale	Common Stock	880	$20.196	$18K
Sale	Common Stock	212	$20.196	$4K
Sale	Common Stock	212	$20.196	$4K
Sale	Common Stock	212	$20.196	$4K
Sale	Common Stock	212	$20.196	$4K
Exercise	Stock option (right to buy)	130	$0.00	--
Exercise	Common Stock	130	$2.39	$310.70
Sale	Common Stock	130	$20.002	$3K
Sale	Common Stock	322	$20.002	$6K
Sale	Common Stock	273	$20.002	$5K
Sale	Common Stock	66	$20.002	$1K
Sale	Common Stock	66	$20.002	$1K
Sale	Common Stock	66	$20.002	$1K
Sale	Common Stock	66	$20.002	$1K
holding	Common Stock	--	--	--
holding	Common Stock	--	--	--
holding	Common Stock	--	--	--

Holdings After Transaction: Stock option (right to buy) — 204 shares (Direct, null); Common Stock — 21,899 shares (Direct, null); Common Stock — 44,781 shares (Indirect, By The Maetzold Descendants 2020 Trust)

Footnotes (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 $20.000 to $20.010, 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. This transaction was executed in multiple trades at prices ranging from $20.005 to $20.350, 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 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

Net shares sold: 4,172 shares Sale price (May 21): $20.196 per share Sale price (May 20): $20.002 per share +5 more

8 metrics

Net shares sold 4,172 shares Open-market sales by Maetzold-related entities in May 2026

Sale price (May 21) $20.196 per share Weighted-average price for several common stock sales

Sale price (May 20) $20.002 per share Weighted-average price for earlier common stock sales

Options exercised 550 shares Stock options converted to common stock on May 20–21, 2026

Option exercise price $2.39 per share Strike price of exercised stock options

Direct holding after trades 21,479 shares Common stock directly held by Maetzold after May 21, 2026 sale

Descendants Trust holding 44,781 shares Common stock held by The Maetzold Descendants 2020 Trust after May 21, 2026

Irrevocable Trust holding 38,061 shares Common stock held by Derek Maetzold 2020 Irrevocable Trust after May 21, 2026

Key Terms

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

5 terms

Rule 10b5-1 plan regulatory

"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.

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.

Stock option (right to buy) financial

"Stock option (right to buy) ... Exercise or conversion of derivative security"

weighted-average sale price financial

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

irrevocable trust financial

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

An irrevocable trust is a legal arrangement where an owner transfers assets into a separate entity managed by a trustee and gives up the power to modify or reclaim those assets. For investors it matters because putting stock or other holdings into such a trust can change who controls and benefits from the assets, affect taxes and creditor protection, and influence how easy it is to sell or value those holdings—like placing valuables in a locked safe overseen by someone else.

Form 4 Insider Transactions: What Each Field Means →

05/22/2026 - 04:12 PM

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).

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)
05/20/2026

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)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	05/20/2026		M⁽¹⁾		130	A	$2.39	21,609	D
Common Stock	05/20/2026		S⁽¹⁾		130	D	$20.002⁽²⁾	21,479	D
Common Stock	05/20/2026		S⁽¹⁾		322	D	$20.002⁽²⁾	45,816	I	By The Maetzold Descendants 2020 Trust⁽³⁾
Common Stock	05/20/2026		S⁽¹⁾		273	D	$20.002⁽²⁾	38,941	I	By Derek Maetzold 2020 Irrevocable Trust⁽⁴⁾
Common Stock	05/20/2026		S⁽¹⁾		66	D	$20.002⁽²⁾	2,158	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk⁽⁵⁾
Common Stock	05/20/2026		S⁽¹⁾		66	D	$20.002⁽²⁾	2,158	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold⁽⁶⁾
Common Stock	05/20/2026		S⁽¹⁾		66	D	$20.002⁽²⁾	2,158	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold⁽⁷⁾
Common Stock	05/20/2026		S⁽¹⁾		66	D	$20.002⁽²⁾	2,158	I	By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold⁽⁸⁾
Common Stock	05/21/2026		M⁽¹⁾		420	A	$2.39	21,899	D
Common Stock	05/21/2026		S⁽¹⁾		420	D	$20.196⁽⁹⁾	21,479	D
Common Stock	05/21/2026		S⁽¹⁾		1,035	D	$20.196⁽⁹⁾	44,781	I	By The Maetzold Descendants 2020 Trust⁽³⁾
Common Stock	05/21/2026		S⁽¹⁾		880	D	$20.196⁽⁹⁾	38,061	I	By Derek Maetzold 2020 Irrevocable Trust⁽⁴⁾
Common Stock	05/21/2026		S⁽¹⁾		212	D	$20.196⁽⁹⁾	1,946	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk⁽⁵⁾
Common Stock	05/21/2026		S⁽¹⁾		212	D	$20.196⁽⁹⁾	1,946	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold⁽⁶⁾
Common Stock	05/21/2026		S⁽¹⁾		212	D	$20.196⁽⁹⁾	1,946	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold⁽⁷⁾
Common Stock	05/21/2026		S⁽¹⁾		212	D	$20.196⁽⁹⁾	1,946	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⁽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)
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)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
Stock option (right to buy)	$2.39	05/20/2026		M⁽¹⁾			130	⁽¹³⁾	11/11/2028	Common Stock	130	$0	624	D
Stock option (right to buy)	$2.39	05/21/2026		M⁽¹⁾			420	⁽¹³⁾	11/11/2028	Common Stock	420	$0	204	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 $20.000 to $20.010, 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 $20.005 to $20.350, 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	05/22/2026
	** 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)

Source: View Original Filing on SEC EDGAR

FAQ

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

CSTL CEO Derek Maetzold reported multiple insider trades where related trusts and a personal account sold 4,172 Castle Biosciences common shares around $20 each, while he also exercised options to acquire 550 shares at $2.39 per share during May 2026.

How many CSTL shares were sold by entities associated with Derek Maetzold?

Entities associated with Derek Maetzold sold 4,172 Castle Biosciences common shares in open-market transactions. These sales were spread across several family-related trusts and a direct holding account, at weighted-average prices near $20.00 and $20.196 per share.

Did Derek Maetzold exercise any Castle Biosciences stock options in this filing?

Yes. Derek Maetzold exercised stock options covering 550 Castle Biosciences shares at an exercise price of $2.39 per share. These derivative exercises converted option rights into additional common shares reflected in his direct holdings after the transactions.

Which trusts linked to Derek Maetzold were involved in the CSTL trades?

The filing lists several involved entities, including The Maetzold 2018 Remainder Trusts for multiple family members, the Derek Maetzold 2020 Irrevocable Trust, The Maetzold Descendants 2020 Trust, and DJM Grantor Retained Annuity Trusts Nos. 5, 6, and 7, each holding CSTL shares.