SEC Form 4 · accession 0001628280-26-063221

CASTLE BIOSCIENCES INC · CSTL

Statement of changes in beneficial ownership, as filed. Original on EDGAR ↗

Reporting owner

Derek J Maetzold

Officer — Pres. & Chief Exec. Officer · Director

Period of report

Sep 21, 2026

Accepted (ET)

Sep 23, 2026 · 4:27 pm EDT

Rule 10b5-1 plan

yes — trade under a plan

Issuer CIK

0001447362

Table I — non-derivative securities

Security	Date	Code	Shares	Price	A/D	Owned after	D/I	Nature of ownership
Common Stock	Sep 21, 2026	M	8,580	$2.39	A	30,059	D
Common Stock^F2	Sep 21, 2026	S	8,580	$35.334	D	21,479	D
Common Stock^F2,F3	Sep 21, 2026	S	3,198	$35.334	D	11,236	I	By The Maetzold Descendants 2020 Trust
Common Stock^F2,F4	Sep 21, 2026	S	2,718	$35.334	D	9,550	I	By Derek Maetzold 2020 Irrevocable Trust
Common Stock^F5	holding	—	—		—	11,256	I	By The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk
Common Stock^F6	holding	—	—		—	11,256	I	By The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold
Common Stock^F7	holding	—	—		—	11,256	I	By The Maetzold 2018 Remainder Trust FBO John Derek Maetzold
Common Stock^F8	holding	—	—		—	11,256	I	By The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold
Common Stock^F9	holding	—	—		—	11,963	I	By DJM Grantor Retained Annuity Trust No. 6
Common Stock^F10	holding	—	—		—	27,862	I	By DJM Grantor Retained Annuity Trust No. 7
Common Stock^F11	holding	—	—		—	40,935	I	By DJM Grantor Retained Annuity Trust No. 8
Common Stock^F12	holding	—	—		—	23,216	I	DJM Grantor Retained Annuity Trust No. 9

Table II — derivative securities

Security	Conv. / exercise price	Date	Code	Shares	A/D	Exercisable	Expires	Underlying	Underlying shares	Owned after	D/I
Stock option (right to buy)^F13	$2.39	Sep 21, 2026	M	8,580	D	—	May 9, 2028	Common Stock	8,580	8,165	D

Explanation of responses

F1These transactions were made pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 2, 2026.
F10Held by DJM Grantor Retained Annuity Trust No. 7 of which the Reporting Person is the trustee and beneficiary.
F11Held by DJM Grantor Retained Annuity Trust No. 8 of which the Reporting Person is the trustee and beneficiary.
F12Held by DJM Grantor Retained Annuity Trust No. 9 of which the Reporting Person is the trustee and beneficiary.
F13The shares subject to the option are fully vested.
F2This 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.
F3Held 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.
F4Held by Derek Maetzold 2020 Irrevocable Trust of which the Reporting Person is the trustee and his children are beneficiaries.
F5Held by The Maetzold 2018 Remainder Trust FBO Emily Carol Kirk of which the Reporting Person is the trustee and his child is the beneficiary.
F6Held by The Maetzold 2018 Remainder Trust FBO Hannah Elizabeth Maetzold of which the Reporting Person is the trustee and his child is the beneficiary.
F7Held by The Maetzold 2018 Remainder Trust FBO John Derek Maetzold of which the Reporting Person is the trustee and his child is the beneficiary.
F8Held by The Maetzold 2018 Remainder Trust FBO Peter Douglas Maetzold of which the Reporting Person is the trustee and his child is the beneficiary.
F9Held 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.