SEC Form S-8 filed by SELLAS Life Sciences Group Inc.

As filed with the Securities and Exchange Commission on June 16, 2026

Registration No. 333-             

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM S-8

REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

SELLAS Life Sciences Group, Inc.

(Exact name of registrant as specified in its charter)

7 Times Square, Suite 2503
New York, NY 10036

(Address of Principal Executive Offices) (Zip Code)

SELLAS Life Sciences Group, Inc. 2026 Second Amended And Restated Equity Incentive Plan

(Full title of the plan)

Angelos M. Stergiou, M.D., ScD h.c.

President and Chief Executive Officer

SELLAS Life Sciences Group, Inc.

7 Times Square, Suite 2503

New York, NY 10036

Telephone: (646) 200-5278

(Name and address of agent for service)

(Telephone number, including area code, of agent for service)

Copies to:

Daniel A. Bagliebter, Esq.

Kostantinos V. Skordalos, Esq.

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

919 Third Avenue, New York, NY 10022 (212) 935-3000

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.

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 7(a)(2)(B) of the Securities Act.

EXPLANATORY NOTE

This Registration Statement on Form S-8 registers 20,000,000 additional shares of common stock, par value $0.0001 per share (“Common Stock”), for issuance under the SELLAS Life Sciences Group, Inc. 2026 Second Amended and Restated Equity Incentive Plan (the “Plan”), representing an increase of 20,000,000 shares reserved under the Plan, as approved by the Registrant’s stockholders at the Registrant’s annual meeting of stockholders on June 16, 2026.

This Registration Statement registers additional securities of the same class as other securities for which the registration statement filed on Form S-8 (File Nos. 333-237168, 333-258799, 333-264899, 333-270608, 333-276615 and 333-289534) of the Registrant is effective. The information contained in the Registrant’s registration statements on Form S-8 filed with the Securities and Exchange Commission on March 13, 2020 (File No. 333-237168), August 13, 2021 (File No. 333-258799), May 12, 2022 (File No. 333-264899), March 16, 2023 (File No. 333-270608), January 19, 2024 (333-276615) and August 12, 2025 (File No. 333-289534) is hereby incorporated by reference pursuant to General Instruction E of Form S-8.

Item 8. Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, New York, on June 16, 2026.

Each person whose signature appears below constitutes and appoints each of Angelos M. Stergiou and John Burns, acting alone or together with another attorney-in-fact, as his true and lawful attorney-in-fact and agent, with full power of substitution and resubstitution, for such person and in his or her name, place and stead, in any and all capacities, to sign any or all further amendments (including post-effective amendments) to this registration statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorney-in-fact and agent, or his or her substitute or substitutes, may lawfully do or cause to be done by virtue hereof. Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement has been signed by the following persons in the capacities and on the date indicated.