Exhibit 99.1 SELLAS Life Sciences Reports Second Quarter 2025 Financial Results and Provides Corporate Update NEW YORK, NY August 12, 2025 -- 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 second quarter ended June 30, 2025, and provided a corporate update. "We continue to make significant progress in adv ...