UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ FORM 10-Q ________________________________ ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2024 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission File Number: 001-33958 SELLAS Life Sciences Group, Inc. (Exact name of registrant as specified in its charter) Delaware 20- ...

Exhibit 99.1 SELLAS Life Sciences Reports Full Year 2023 Financial Results and Provides Corporate Update NEW YORK, March 28, 2024 – SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) ("SELLAS'' or the "Company"), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the full year ended December 31, 2023, and provided a corporate update. "We are off to a strong start this year highlighted by prog ...

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ FORM 10-K ________________________________ (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2023 or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from _________ to _________ Commission File Number: 001-33958 SELLAS Life Sciences G ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ FORM 10-Q ________________________________ For the quarterly period ended September 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission File Number: 001-33958 SELLAS Life Sciences Group, Inc. 7 Times Square, Suite 2503, New York, NY 10036 ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 (Exact name of r ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission File Number: 001-33958 SELLAS Life Sciences Group, Inc. (Exact name of registrant as specified in its charter) Delaware 20-8099512 (State of incorporation) (I.R.S. Employer Identification No.) FORM 10-Q ________________________________ ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ FORM 10-Q ________________________________ ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission File Number: 001-33958 SELLAS Life Sciences Group, Inc. (Exact name of registrant as specified in its charter) Delaware 20- ...

(Mark One) Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ FORM 10-K ________________________________ ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2022 or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from _________ to _________ Commission File Number: 001-33958 SELLAS Life Sciences G ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ FORM 10-Q ________________________________ ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2022 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission File Number: 001-33958 SELLAS Life Sciences Group, Inc. (Exact name of registrant as specified in its charter) Delaware ...

ZELLAS CELLAS | --- | --- | --- | --- | --- | --- | --- | |----------------|------------------|-------|-------|-------|-------|-------| | | | | | | | | | | | | | | | | | | | | | | | | | | Company Overview | | | | | | | NASDAQ: SLS | | | | | | | | | | | | | | | | September 2022 | | | | | | | | | | | | | | | Forward Looking Statements This presentation contains forward-looking statements. Such forward-looking statements can be identified by the use of the words "expect," "believe," "will," "anticipate," "esti ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 ________________________________ FORM 10-Q ________________________________ ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2022 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission File Number: 001-33958 SELLAS Life Sciences Group, Inc. (Exact name of registrant as specified in its charter) Delaware 20-8099 ...