As filed with the U.S. Securities and Exchange Commission on June 24, 2020.

Registration No. 333-239354

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST EFFECTIVE AMENDMENT NO.1 TO

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Castle Biosciences, Inc.

(Exact Name of Registrant as Specified in Its Charter)

Delaware	8071	77-0701774
(State or Other Jurisdiction of Incorporation or Organization)	(Primary Standard Industrial Classification Code Number)	(I.R.S. Employer Identification Number)

820 S. Friendswood Drive, Suite 201

Friendswood, Texas 77546

(866) 788-9007

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Derek Maetzold

President and Chief Executive Officer

Castle Biosciences, Inc.

820 S. Friendswood Drive, Suite 201

Friendswood, Texas 77546

(866) 788-9007

(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

Copies to:

Thomas A. Coll, Esq. Karen E. Deschaine, Esq. Cooley LLP 4401 Eastgate Mall San Diego, California 92121 (858) 550-6000 Peter N. Handrinos, Esq. Wesley Holmes, Esq. Anthony Gostanian, Esq. Latham & Watkins LLP 200 Clarendon Street Boston, Massachusetts 02116 (617) 880-4500

Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☒ (File No. 333-239354)

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	☐	Accelerated filer	☐
Non-accelerated filer	☒	Smaller reporting company	☒
		Emerging growth company	☒

If an emerging growth company, indicate by check mark if the registrant has not elected to use the extended transition period for complying with any new or revised financial accounting standards provided in Section 7(a)(2)(B) of the Securities Act. ☐

This post-effective amendment shall become effective upon filing in accordance with Rule 462(d) promulgated under the Securities Act of 1933, as amended.

EXPLANATORY NOTE

This Post-Effective Amendment No. 1 (this “Amendment”) relates to the Registrant’s Registration Statement on Form S-1 (File No. 333-239354) declared effective on June 24, 2020 by the Securities and Exchange Commission. The Registrant is filing this Amendment for the sole purpose of replacing Exhibit 5.1 to the Registration Statement. This Amendment does not modify any provision of Part I or Part II of the Registration Statement other than Item 16(a) of Part II as set forth below.

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 16. Exhibits and Financial Statement Schedules.

(a) Exhibits

Exhibit Number	Description
5.1	Opinion of Cooley LLP.
23.1	Consent of Cooley LLP (included in Exhibit 5.1).
24.1	Power of Attorney (included on the signature page of the Registration Statement on Form S-1 (File No. 333-239354), filed with the Commission on June 22, 2020 and incorporated herein by reference).

SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant has duly caused this Post-Effective Amendment No.1 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Friendswood, State of Texas, on the 24^th day of June, 2020.

CASTLE BIOSCIENCES, INC.
By:	/s/ Derek J. Maetzold
	Derek J. Maetzold
	President and Chief Executive Officer

Pursuant to the requirements of the Securities Act, this Post-Effective Amendment No.1 to the Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

Signature	Title	Date
/s/ Derek J. Maetzold	President, Chief Executive Officer and Member of the Board of Directors (Principal Executive Officer)	June 24, 2020
Derek J. Maetzold
/s/ Frank Stokes	Chief Financial Officer (Principal Financial and Accounting Officer)	June 24, 2020
Frank Stokes
*	Chairman of the Board of Directors	June 24, 2020
Daniel M. Bradbury
*	Member of the Board of Directors	June 24, 2020
Bonnie H. Anderson
*	Member of the Board of Directors	June 24, 2020
Mara Aspinall
*	Member of the Board of Directors	June 24, 2020
G. Bradley Cole
*	Member of the Board of Directors	June 24, 2020
Joseph C. Cook III
*	Member of the Board of Directors	June 24, 2020
Miles D. Harrison
*	Member of the Board of Directors	June 24, 2020
David Kabakoff, Ph.D.

*By:	/s/ Derek J. Maetzold
	Derek J. Maetzold Attorney-in-fact