SELLAS Life Sciences Group, Inc.

On June 17, 2025, we held our Annual Meeting of Stockholders, or the Annual Meeting. As previously reported in our Current Report on Form 8-K filed on June 18, 2025, at the Annual Meeting, our stockholders cast the greatest number of votes in favor of holding future non-binding advisory stockholder votes on executive officer compensation, or Say-on-Pay votes, every year. The Board has determined that, consistent with the vote of the Company's stockholders and the Board's recommendation in the Proxy Statement for the Annual Meeting, the Company will continue to hold future Say-on-Pay votes every year until the next required stockholder vote on the frequency of Say-on-Pay votes is presented to the stockholders.

None of our directors or officers have adopted, modified, orterminated any trading plans under Rule 10b5-1 of the Exchange Act or any similar arrangements during the three months ended June 30, 2025.