UNITED STATES ~~SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549~~

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT ~~REPORTPURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934~~ REPORT

~~Date~~PURSUANT ofTO ~~report~~SECTION ~~(Date~~13 ofOR ~~earliest event reported~~15(d): ~~May~~OF ~~12, 2026~~THE

SECURITIES EXCHANGE ACT OF 1934

Date of report (Date of earliest event reported): June 2, 2026

SELLAS Life Sciences Group, Inc.

(Exact name of registrant as specified in its charter)

Delaware

001-33958

20-8099512

~~001-33958~~

~~20-8099512~~

(State or other jurisdiction of incorporation or organization)

(Commission File Number)

(I.R.S. Employer Identification No.)

~~(CommissionFile Number)~~

~~(I.R.S. EmployerIdentification No.)~~

7 Times Square, Suite 2503New York, NY 10036

7 Times Square, Suite 2503 New York, NY 10036

(Address of Principal Executive Offices) (Zip Code)

~~(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 28.~~02.~~01 ~~Results~~Other ~~of Operations and Financial Condition.~~Events

OnAs ~~May~~previously 12reported, ~~2026~~as of March 31, 2026, SELLAS Life Sciences Group, Inc. (~~“SELLAS”) issued a press release (~~the “~~Press Release~~Company”) ~~announcing~~had ~~its~~$107.1 ~~financial~~million ~~results~~of ~~for~~cash ~~the quarter ended March 31, 2026~~ and ~~providing~~cash ~~a corporate update~~equivalents.

ASubsequent ~~copy of the Press Release is furnished hereto as Exhibit 99.1 and is incorporated by reference herein. The information contained in this Item 2.02 and in the Press Release furnished as Exhibit 99.1~~ to ~~this~~March ~~Current Report on Form 8-K shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934~~31, ~~as amended~~2026, orin ~~otherwise~~April ~~subject to the liabilities of that Section or Sections 11~~ and ~~12(a)(2)~~May 2026, of the ~~Securities~~Company ~~Act~~received ofapproximately ~~1933, as amended~~$28.7 ~~The~~million ~~information contained~~ in ~~this~~proceeds ~~Item~~from ~~2.02 and in~~ the ~~Press~~exercise Release furnished as Exhibit 99.1 to this Current Report on Form 8-K shall not be incorporated by reference into any filing with the SEC made by SELLAS whether made before or after the date hereof, regardless of ~~any~~common ~~general~~stock ~~incorporation language in such filing~~warrants.

As of June 2, 2026, the Company had 196,632,574 shares of common stock outstanding.

Item 9.01.

Financial Statements and Exhibits.

(d) Exhibits

Exhibit Number	Description	~~Description~~
99.1		Press Release dated May 12, 2026
104	Cover Page Interactive Data File (embedded within the Inline XBRL document)
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.

~~SELLAS Life Sciences Group, Inc.~~

Date:

June 2, 2026

By:

/s/ John T. Burns

~~May 12, 2026~~

~~By:~~

~~/s/ John T. Burns~~

Name:

John T. Burns

~~Name:~~

~~John T. Burns~~

Title:

Senior Vice President, Chief Financial Officer

~~Title:~~

~~Senior Vice President, Chief Financial Officer~~

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