RTW Investments reveals 7.2% Castle Biosciences (CSTL) stake in 13G filing

Rhea-AI Filing Summary

Castle Biosciences, Inc. has a new large shareholder disclosure. RTW Investments, LP and its managing partner, Roderick Wong, M.D., report beneficial ownership of 2,115,237 shares of Castle Biosciences common stock, representing 7.2% of the company’s outstanding shares based on 29,188,659 shares outstanding as of October 27, 2025.

The shares are held by funds advised by RTW Investments, which have the right to receive dividends and sale proceeds. The filing states the position is held in the ordinary course of business and not for the purpose of changing or influencing control of Castle Biosciences.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

CASTLE BIOSCIENCES, INC.

(Name of Issuer)

Common Stock, $0.001 par value

(Title of Class of Securities)

14843C105

(CUSIP Number)

12/31/2025

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13G

CUSIP No. 14843C105

1

Names of Reporting Persons

RTW Investments, LP

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 2,115,237.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,115,237.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,115,237.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.2 %

12

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13G

CUSIP No. 14843C105

1

Names of Reporting Persons

Roderick Wong

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 2,115,237.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,115,237.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,115,237.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.2 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: CASTLE BIOSCIENCES, INC.
(b)	Address of issuer's principal executive offices: 505 S. Friendswood Drive, Suite 401, Friendswood, TX, 77546.
Item 2.
(a)	Name of person filing: This statement is filed by: (i) RTW Investments, LP ("RTW Investments"), a Delaware limited partnership and the investment adviser to certain funds (the "RTW Funds"), with respect to shares of Common Stock, par value $0.001 per share (the "Shares") of Castle Biosciences, Inc. (the "Company") directly held by the RTW Funds; and (ii) Roderick Wong, M.D. ("Dr. Wong"), the Managing Partner and Chief Investment Officer of RTW Investments, with respect to the Shares directly held by the RTW Funds. The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons." The filing of this statement should not be construed as an admission that any of the foregoing persons or any Reporting Person is, for the purposes of Section 13 of the Securities Exchange Act of 1934, as amended, the beneficial owner of the Shares reported herein.
(b)	Address or principal business office or, if none, residence: The address of the business office of each of the Reporting Persons is 40 10th Avenue, Floor 7, New York, New York 10014.
(c)	Citizenship: RTW Investments is a Delaware limited partnership. Dr. Wong is a citizen of the United States.
(d)	Title of class of securities: Common Stock, $0.001 par value
(e)	CUSIP No.: 14843C105
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: The information required by Item 4(a) is set forth in Rows 5 - 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentages set forth in Row 11 of the cover pages are calculated based upon 29,188,659 Shares outstanding as of October 27, 2025 as reported in the Company's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 3, 2025.
(b)	Percent of class: RTW Investments: 7.2% Dr. Wong: 7.2%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: RTW Investments: 0 Dr. Wong: 0
	(ii) Shared power to vote or to direct the vote: RTW Investments: 2,115,237 Shares Dr. Wong: 2,115,237 Shares
	(iii) Sole power to dispose or to direct the disposition of: RTW Investments: 0 Dr. Wong: 0
	(iv) Shared power to dispose or to direct the disposition of: RTW Investments: 2,115,237 Shares Dr. Wong: 2,115,237 Shares
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. See Item 2. The RTW Funds have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares reported herein.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

RTW Investments, LP

Signature:	/s/ Roderick Wong, M.D.
Name/Title:	Roderick Wong, M.D., Managing Partner
Date:	02/17/2026

Roderick Wong

Signature:	s/ Roderick Wong, M.D.
Name/Title:	Roderick Wong, M.D.
Date:	02/17/2026

Exhibit Information

Exhibit 99.1 Joint Filing Agreement

FAQ

What stake in Castle Biosciences (CSTL) does RTW Investments report?

RTW Investments reports beneficial ownership of 2,115,237 shares of Castle Biosciences common stock, representing 7.2% of the outstanding shares. This makes RTW a significant institutional shareholder in CSTL based on the company’s reported share count.

Who is the individual associated with the Castle Biosciences (CSTL) Schedule 13G filing?

The filing names Roderick Wong, M.D., Managing Partner and Chief Investment Officer of RTW Investments, as a reporting person. He is reported to share voting and dispositive power over the same 2,115,237 Castle Biosciences shares held by RTW-advised funds.

How much of Castle Biosciences’ share count is used to calculate RTW’s 7.2% ownership?

The reported 7.2% ownership is calculated using 29,188,659 shares of Castle Biosciences common stock outstanding as of October 27, 2025, as disclosed in the company’s Form 10-Q. This baseline determines RTW’s percentage stake.

Do RTW Investments and Roderick Wong hold Castle Biosciences (CSTL) shares to influence control?

The filing states the securities were acquired and are held in the ordinary course of business and not for the purpose of changing or influencing control of Castle Biosciences. It also notes they are not held in connection with any control-seeking transaction.

Who has economic rights to the Castle Biosciences (CSTL) shares reported in the 13G?

The filing explains that certain RTW Funds directly hold the Castle Biosciences shares. These funds have the right to receive dividends or proceeds from any sale of the reported shares, while RTW Investments acts as their investment adviser.

What type of SEC filing did RTW Investments make regarding Castle Biosciences (CSTL)?

RTW Investments and Roderick Wong filed a Schedule 13G, a beneficial ownership report for passive holders of more than 5% of a company’s stock. It discloses their 7.2% stake in Castle Biosciences common shares and related ownership details.