SELLAS Life Sciences Reaches 80th Event in Phase 3 REGAL Trial of Galinpepimut-S (GPS) in Acute Myeloid Leukemia

SELLAS Life Sciences Reaches 80th Event in Phase 3 REGAL Trial of Galinpepimut-S (GPS) in Acute Myeloid Leukemia

- Reaching the Pre-Specified 80 th Event Triggers the Final Analysis of the Pivotal Phase 3 Trial -

- Company to Report Topline Primary Endpoint Results this Quarter -

NEW YORK, Oct. 28, 2026 (GLOBE NEWSWIRE) -- 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 announced that the pivotal Phase 3 REGAL trial evaluating galinpepimut-S (GPS) in patients with acute myeloid leukemia (AML) has reached the pre-specified 80 th event (number of deaths), triggering the final analysis of the study.

The REGAL trial is an event-driven overall survival study, and with the occurrence of the 80 th event, SELLAS will proceed with database lock, unblinding of the study data, and statistical analysis of the primary endpoint data. Upon completion of this analysis, the Company will announce this quarter the preliminary topline primary endpoint results from the trial in accordance with the study’s pre-specified statistical analysis plan (SAP).

“Reaching the 80 th event represents a critical milestone in the REGAL trial,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “AML remains an area of significant unmet need, particularly for patients in second complete remission with limited treatment options. With this pivotal study now advancing to final analysis, we look forward to evaluating the data, as positive results could position GPS as the first- and best-in-class novel immunotherapeutic option for these patients. On behalf of everyone at SELLAS, my sincerest appreciation goes out to all the physicians, nurses, study teams and, importantly, the participating patients and their families for their immense contributions in advancing the REGAL study. Our commitment to delivering hope to the AML community has never been stronger.”

About Phase 3 REGAL Trial

The Phase 3 REGAL trial (NCT04229979) is a randomized registrational clinical trial evaluating GPS as a potential maintenance therapy in AML patients who have achieved a second complete remission (CR2). The primary endpoint of the study is overall survival with secondary endpoints including leukemia-free survival and other clinical outcomes.

About SELLAS Life Sciences Group, Inc.

SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com .

Forward-Looking Statements

This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS and SLS009 clinical development programs, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 19, 2026 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made.

Investor Contact

John Fraunces Managing Director LifeSci Advisors, LLC [email protected]

Media Contact

Joan Bosisio VP, Scientific & Medical Communications Simpson Healthcare [email protected]

Source: SELLAS Life Sciences Group, Inc.