Valemetostat Therapy for Relapsed Adult T-Cell Leukemia/Lymphoma After Allogeneic Hematopoietic Stem Cell Transplantation

This retrospective study evaluated 11 patients who received valemetostat, a novel selective dual inhibitor of the enhancer of zeste homologs 1 and 2, as a salvage therapy for relapsed adult T-cell leukemia/lymphoma after allogeneic hematopoietic cell transplantation (allo-HCT). The median age of the patients at allo-HCT was 64 (range: 43–70) years. The median interval between allo-HCT and valemetostat therapy was 210 (range: 35–682) days. The median lactate dehydrogenase and soluble interleukin-2 receptor levels were 238 (range: 184–298) U/L and 818 (range: 435–2193) U/mL, respectively. Eight patients initially received valemetostat at a reduced dose because of thrombocytopenia. The median treatment duration was 156 (range: 39–645) days, with five patients continuing treatment. The best response rate was 73%, including clinical responses (complete or partial response) in six patients and molecular responses defined by clearance of blood measurable residual disease in two patients. The reasons for treatment discontinuation were adverse events (cytomegalovirus infection, pericardial effusion, and dysgeusia) (n = 3) and progressive disease (n = 3). None of the patients developed graft-versus-host disease. The median overall survival after valemetostat therapy was 294 (range: 56–645) days. At the last follow-up, four patients were alive without disease, four were alive with disease, and three died due to progressive disease. Hence, valemetostat is a promising salvage therapy for relapsed adult T-cell leukemia/lymphoma after allo-HCT.