Steering Committee Update Provided on Phase 3 REGAL Study in addition to Positive Topline Data Announcement from the Phase 2a Study of SLS009 in R/R AML

“Completion of enrollment in the Phase 3 REGAL trial represents an important milestone in our goal to deliver GPS to AML patients,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “We are extremely grateful to the patients, their families, and investigators who have helped us achieve this significant milestone. Additionally, we are pleased to share that the Steering Committee has reviewed the study as of the March 1, 2024, cutoff date. As of this evaluation, 123 patients were enrolled with 66 of them discontinuing the treatment. In the trial, patients are recorded as having stopped the study treatment in cases of death for any reason, relapse, intolerable toxicity, or treatment completion. Regarding the GPS arm, we are pleased to report that we have not observed any intolerable toxicities in any patient population across all our clinical studies thus far, although toxicities are commonly observed with therapies used in the control arm. Therefore, almost all patients who are off treatment may have most likely either relapsed or passed away. The most frequent cause of death in this patient population is relapse. As the study sponsors, we lack specific information on the outcomes of these 66 patients, hindering our ability to confirm whether the required number of events for interim analysis – 60 – has been reached. The determination of such outcomes, the primary endpoint of the trial, lies within the purview of the IDMC, which is now scheduled to meet by the end of April.”