SLS SELLAS Life Sciences Group Inc

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 3D Medicines Inc., SELLAS’ licensee for the development and commercialization of its lead clinical candidate, galinpepimut-S (GPS), in China, Hong Kong, Macau and Taiwan, has dosed the first patient in its Phase 1 clinical trial in China of GPS (3D189 in China).

The Phase 1 clinical trial is an open-label, single-arm, multi-center study in patients with acute myeloid leukemia in complete response, or patients with multiple myeloma, non-Hodgkin’s lymphoma or higher-risk myelodysplastic syndrome who have received at least first-line standard therapy and achieved a complete response or partial response. 3D Medicines plans to recruit fifteen patients for the study.

“The dosing of the first patient in 3D Medicines’ Phase 1 clinical trial for GPS, or 3D189, in China, marks an important milestone for GPS’ global clinical development. We are excited that 3D Medicines’ clinical program for GPS is proceeding on course, and we look forward to receiving the results from this study,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS.

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, galinpepimut-S (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 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 GFH009, a small molecule, highly selective CDK9 inhibitor, which is licensed from GenFleet Therapeutics (Shanghai), Inc., for all therapeutic and diagnostic uses in the world outside of Greater China.

For more information on SELLAS, please visit www.sellaslifesciences.com.

About 3D Medicines Inc. 3D Medicines Inc. is a commercial-stage biopharmaceutical company with a mission to help people with cancer live longer and better. Envisioning a future when cancer is managed as a chronic disease, 3D Medicines focuses on the development of differentiated next-generation immuno-oncology drugs, helping cancer patients live with prolonged survival time and a better quality of life. 3D Medicines has established a pipeline with both next-generation biological macromolecule and chemotherapeutic small-molecule drugs, as well as a professional team capable of global development, registration and commercialization operation.

For more information, please visit http://www.3d-medicines.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 global clinical development of GPS and the potential for GPS as a drug development candidate. 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 associated with the COVID-19 pandemic and its impact on the Company’s clinical plans and business strategy, risks and uncertainties associated 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 31, 2022 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 Allison Soss KCSA Strategic Communications Email: SELLAS@kcsa.comPhone: 212.896.1267

Media Contacts Raquel Cona / Michaela Fawcett KCSA Strategic Communications Email: SELLAS@kcsa.comPhone: 212.896.1276