SELLAS Life Sciences Group to Host Virtual R&D Day on October 29, 2025: Advancing Novel Therapies in Acute Myeloid Leukemia (AML): An Overview of the Ongoing Phase 3 REGAL Trial of Galinpepimut-S (GPS) and SLS009 Program Update

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 it will host a virtual R&D Day on Wednesday, October 29, 2025 at 10:00 AM ET featuring key opinion leaders (KOLs), alongside company management, to discuss the unmet medical need and evolving treatment landscape for acute myeloid leukemia (AML). To register, click here.

The event will feature an overview of the ongoing Phase 3 REGAL trial of GPS (results expected by year-end) and a discussion of the unmet needs of AML patients in complete second remission (CR2). SELLAS will also present an update of SLS009, its highly selective cyclin-dependent kinase 9 (CDK9) inhibitor, highlighting recently reported Phase 2 data and plans for a newly diagnosed and frontline AML study anticipated to begin in the first quarter of 2026.

A live Q&A session will follow the formal presentations.

About Omer Jamy, MD Omer Jamy, MD is Assistant Professor of Medicine at the University of Alabama (UAB) in the Division of Hematology and Oncology and Associate Scientist, Experimental Therapeutics at the O'Neal Comprehensive Cancer Center. He serves as principal investigator of the Phase 3 REGAL study at UAB, one of the trial’s highest enrolling sites, and leads several clinical trials in addition to REGAL, focusing on AML, chronic myelogenous leukemia, and allogeneic stem cell transplantation. Dr. Jamy completed his internal medicine residency at the University of Tennessee in Memphis followed by fellowship training at UAB in hematology/oncology, bone marrow transplantation and cellular therapy.

About Panagiotis Tsirigotis, MD, PhD Panagiotis Tsirigotis, MD, PhD is Professor of Hematology at the National and Kapodistrian University of Athens, School of Medicine in Athens, Greece, and Scientific Director of the Transplantation Program of the Hematology Unit since 2010. He is an investigator in the Phase 3 REGAL trial and has enrolled the highest number of patients in the study. His clinical work focuses on AML with particular emphasis on cellular therapies and hematopoietic cell transplantation. Dr. Tsirigotis' research focuses on the application of immunotherapy methods to prevent leukemia relapse after allogeneic transplantation, such as the administration of donor lymphocytes, as well as on mechanisms of immune escape in hematologic malignancies. He is the president of Acute Leukemia Working Party of the Hellenic Society of Hematology, and Vice President of the Hellenic Transplant Organization.

About Philip Amrein, MD Philip Amrein, MD is Assistant Professor of Medicine at Harvard Medical School and a physician at the Massachusetts General Hospital (MGH), where he is part of the Cancer Center, Leukemia, Cellular Immunotherapy, and Hematology/Oncology departments. Dr. Amrein specializes in treating adults with acute and chronic leukemias, myelodysplasia, and myeloproliferative neoplasms, and leads numerous clinical trials exploring novel treatment approaches. Dr. Amrein has conducted research with SLS009 and is an expert in cyclin-dependent kinases (CDK).

About Sharif Khan, MD Sharif Khan, MD is a hematologist at Bon Secours Health System in Greenville, SC. He is a highly rated specialist in indications such as AML, myeloproliferative neoplasms, multiple myeloma, non-Hodgkin lymphoma, and bone marrow transplantation. In addition to clinical care, Dr. Khan is a researcher for cutting-edge, breakthrough therapies and started a CAR T-Cell program at Bon Secours Health System. Dr. Khan serves as an investigator in both the REGAL trial of GPS and the SLS009 clinical program.

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 our ability to close the offering, the gross proceeds from the offering and the expected use of proceeds. 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 20, 2025 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]