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 3, 2025

SELLAS Life Sciences Group, Inc.

(Exact name of registrant as specified in its charter)

Delaware	001-33958	20-8099512
(State or other jurisdiction of incorporation or organization)	(Commission File Number)	(I.R.S. Employer Identification No.)

	7 Times Square, Suite 2503 New York, NY 10036
	(Address of Principal Executive Offices) (Zip Code)

Registrant’s telephone number, including area code: (646) 200-5278

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

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class	Trading symbol(s)	Name of each exchange on which registered
Common Stock, $0.0001 par value per share	SLS	The Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company 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. ¨

Item 4.01 Changes in Registrant’s Certifying Accountant

On June 3, 2025, SELLAS Life Sciences Group, Inc.’s (the “Company”) independent registered public accounting firm, Moss Adams LLP (“Moss Adams”), merged with Baker Tilly US, LLP. The combined audit practices operate as Baker Tilly US, LLP (“Baker Tilly”). In connection with the merger, Moss Adams has resigned as the auditors of the Company and on June 3, 2025, the Audit Committee of the Company’s Board of Directors accepted the resignation of Moss Adams and approved the appointment of Baker Tilly, as the successor to Moss Adams, as the Company’s independent registered public accounting firm.

The audit report of Moss Adams on the Company’s consolidated financial statements as of and for the years ended December 31, 2024 and 2023, did not contain an adverse opinion or a disclaimer of opinion, nor were they qualified or modified as to uncertainty, audit scope or accounting principles. Moss Adams’ audit report on the consolidated financial statements contained an explanatory paragraph regarding a going concern uncertainty.

During the fiscal years ended December 31, 2024 and 2023, and the subsequent interim period through the date of this Current Report on Form 8-K, there were no (a) disagreements within the meaning of Item 304(a)(1)(iv) of Regulation S-K with Moss Adams on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure, which, if not resolved to Moss Adams’ satisfaction, would have caused it to make reference to the subject matter of the disagreement in connection with its reports on the Company’s financial statements, and (b) reportable events within the meaning of Item 304(a)(1)(v) of Regulation S-K.

On June 3, 2025, the Company engaged Baker Tilly as the Company’s new independent registered public accounting firm for the fiscal year ending December 31, 2025.

During the fiscal years ended December 31, 2024 and 2023, and the subsequent interim period through the date of this Current Report on Form 8-K, neither the Company, nor anyone on its behalf, consulted with Baker Tilly regarding: (i) either the application of accounting principles to a specified transaction, either completed or proposed, or the type of audit opinion that might be rendered on the Company’s financial statements; (ii) any matter that was either the subject of a “disagreement,” as defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions to that item, or (iii) any reportable event within the meaning of Item 304(a)(1)(v) of Regulation S-K.

The Company provided Moss Adams with a copy of this Current Report on Form 8-K prior to its filing with the Securities and Exchange Commission (the “Commission”) and requested that Moss Adams furnish the Company with a letter addressed to the Commission stating whether it agrees with the above statements and, if it does not agree, the respects in which it does not agree. A copy of Moss Adams’ letter to the Commission, dated June 6, 2025, is filed as Exhibit 16.1 to this Form 8-K and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit Number		Description
16.1		Letter from Moss Adams Dated June 6, 2025
104		Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

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

	SELLAS Life Sciences Group, Inc.

Date: June 6, 2025	By:	/s/ John T. Burns
		Name:	John T. Burns
		Title:	Senior Vice President, Chief Financial Officer

SELLAS Life Sciences Group, Inc. 8-K