[Form 4] CASTLE BIOSCIENCES INC Insider Trading Activity

Rhea-AI Filing Summary

Derek J. Maetzold, President & Chief Executive Officer and a director of Castle Biosciences, sold 1,339 shares of Castle Biosciences common stock on 09/17/2025 under a preexisting Rule 10b5-1 plan at a weighted-average price of $21.971 per share. After the sale, the filing reports Mr. Maetzold directly or indirectly beneficially owns multiple blocks of shares held in various trusts, with specific reported holdings including 65,666 shares directly and several trust holdings (for example, 52,923; 44,986; multiple 3,615–3,618 blocks; and larger grantor retained annuity trusts of 85,959; 18,718; and 44,323).

The Form 4 explains the sale was effected through multiple trades at prices ranging from $21.860 to $22.085 and that the transactions were executed pursuant to a 10b5-1 plan adopted May 8, 2025. The form is signed by an attorney-in-fact on behalf of the reporting person.

Positive

• Transaction executed under a Rule 10b5-1 plan, indicating the sale was preplanned (adopted May 8, 2025)
• Price range disclosed ($21.860 to $22.085) with weighted-average sale price of $21.971
• Detailed trust-level beneficial ownership disclosed, enhancing transparency about insider holdings

Negative

• Insider sale of 1,339 shares reduced direct holdings reported on the Form 4
• Significant beneficial ownership concentrated in related trusts, which may indicate continued insider control or limited public float influence

Insights

Financial Analyst

TL;DR: Insider used a preplanned 10b5-1 program to sell a small block of shares; holdings remain substantially concentrated in trusts.

The reported sale of 1,339 shares at a weighted-average $21.971 per share appears to be a routine disposition under a Rule 10b5-1 plan adopted May 8, 2025, reducing direct ownership but leaving significant beneficial holdings across multiple trusts. The disclosure of trade price range ($21.860–$22.085) and the explicit 10b5-1 reference supports that the transaction was prearranged rather than opportunistic. For investors, the material datapoints are the executed sale volume and the detailed breakdown of trust holdings which show continued concentrated insider exposure.

Corporate Governance Expert

TL;DR: Use of a documented 10b5-1 plan and full trust disclosures aligns with good reporting practice; sale is modest versus aggregate holdings.

The Form 4 provides the necessary transparency by identifying the 10b5-1 plan adoption date and specifying the nature of indirect holdings through named trusts and beneficiaries. The seller remains a trustee or related party to multiple trusts, indicating ongoing control or influence over sizeable positions. The filing is procedurally complete and signed by an attorney-in-fact, consistent with accepted governance processes for insider transactions.

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).

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)
09/17/2025

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	09/17/2025		S(1)		1,339	D	$21.971(2)	65,666	D
Common Stock								52,923	I	By The Maetzold Descendants 2020 Trust(3)
Common Stock								44,986	I	By Derek Maetzold 2020 Irrevocable Trust(4)
Common Stock								3,618	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk(5)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold(6)
Common Stock								3,615	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold(7)
Common Stock								3,615	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

Explanation of Responses:

1. These transactions were made pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on May 8, 2025.

2. This transaction was executed in multiple trades at prices ranging from $21.860 to $22.085, 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.

Remarks:

	/s/ Frank Stokes, Attorney-in-fact	09/19/2025
	** 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 did Castle Biosciences (CSTL) insider Derek Maetzold report on Form 4?

The Form 4 reports that Derek J. Maetzold sold 1,339 shares on 09/17/2025 under a Rule 10b5-1 plan at a weighted-average price of $21.971 per share.

Was the sale part of a preplanned trading program?

Yes. The filing states the transactions were made pursuant to a Rule 10b5-1 plan adopted May 8, 2025.

What price range was disclosed for the executed trades?

The trades were executed at prices ranging from $21.860 to $22.085; the weighted-average price reported is $21.971.

How much beneficial ownership does the filing show after the transaction?

The filing lists 65,666 shares as beneficially owned following the reported transaction and additional indirect holdings across multiple trusts (examples: 52,923; 44,986; 85,959; 44,323; 18,718).

Who signed the Form 4 filing?

The Form 4 is signed by Frank Stokes, Attorney-in-fact on behalf of the reporting person on 09/19/2025.