SELLAS Announces U.S. FDA Rare Pediatric Disease Designation Granted to SLS009 for the Treatment of Pediatric Acute Lymphoblastic Leukemia

SELLAS Life Sciences Group, Inc.

- Acute Lymphoblastic Leukemia (ALL) is the Most Common Type of Cancer in Children –

- Rare Pediatric Disease Designation (RPDD) Provides Eligibility for SLS009 to Receive a Priority Review Voucher (PRV) Upon Marketing Approval that can be Transferred/Sold to Other Parties –

- Past Sales of PRVs Have Averaged More Than $100 Million -

NEW YORK, June 24, 2024 (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 U.S. Food and Drug Administration (FDA) has granted Rare Pediatric Disease Designation (RPDD) to SLS009, a highly selective CDK9 inhibitor, for the treatment of pediatric acute lymphoblastic leukemia (ALL).

“We are pleased that the FDA has granted Rare Pediatric Disease Designation to SLS009 for the treatment of pediatric ALL, the most common cancer diagnosed in children,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. ”We remain steadfast in our commitment to advancing SLS009 through the clinical development process across multiple indications and striving to improve the lives of patients, including children, and their families affected by ALL. We look forward to exploring SLS009 as a potential treatment option in pediatric ALL and this designation will significantly help expedite clinical development.”

Childhood ALL is a life-threatening disease with a high unmet medical need. Despite significant advances in the treatment of pediatric ALL, relapse continues to be the most common cause of treatment failure. There are patient subpopulations with high-risk and very high-risk features in need of less toxic therapies that would ultimately extend their long-term event-free survival (EFS) which remains around 50% for very high-risk groups. In clinical trials, SLS009 has demonstrated a very favorable safety profile with complete absence, to date, of any non-hematologic clinical higher-grade toxicities.

Rare Pediatric Disease (RPD) Designation is granted by the FDA for serious or life-threatening diseases that affect fewer than 200,000 people in the United States, and in which the serious or life-threatening manifestations primarily affect individuals less than 18 years of age. If, in the future, a New Drug Application (NDA) for SLS009 for the treatment of pediatric AML is approved by the FDA, SELLAS might be eligible to receive a Priority Review Voucher (PRV) that could be redeemed to receive a priority review for any subsequent marketing application. PRVs may be used by the sponsor or sold to another sponsor for their use and have recently sold for approximately $100 million.

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’ other 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 (formerly GFH009) - 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 clinical development program, 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 28, 2024 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

Bruce Mackle

Managing Director

LifeSci Advisors, LLC

SELLAS@lifesciadvisors.com