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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): June 24, 2020

Castle Biosciences, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (866) 788-9007

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b–2 of the Securities Exchange Act of 1934 (§240.12b–2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

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Item 8.01 Other Events.

On June 24, 2020, Castle Biosciences, Inc. (the “Company”), entered into an underwriting agreement with SVB Leerink LLC and Robert W. Baird & Co. Incorporated, as representatives of the several underwriters named in Schedule A thereto (the “Underwriters”), relating to the public offering of 2,000,000 shares of the Company’s common stock. The public offering price of each share of common stock was $37.00. The offering closed on June 29, 2020. The Underwriters have an option to purchase up to an additional 300,000 share of common stock at the public offering price, less underwriting discounts and commissions, through July 24, 2020.

The gross proceeds to the Company, before deducting underwriting discounts and commissions and other offering expenses, were $74.0 million.

The offering was made only by means of a prospectus forming a part of the effective registration statements (File Nos. 333-239354 and 333-239418) relating to the offering of these securities.

The disclosures in this Current Report on Form 8-K shall not constitute an offer to sell or a solicitation of an offer to buy, nor shall there be any offer or sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of such state or jurisdiction.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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