Daiichi Sankyo Company, Limited announced that new data for valemetostat, a potential first-in-class specific and potent dual inhibitor of EZH1 and EZH2, showed promising and durable tumor response in patients with relapsed/refractory peripheral T-cell lymphoma (PTCL) and adult T-cell leukemia/lymphoma (ATL).1,2 The data were reported on June 11, 2021 during an oral presentation (Abstract #S218) at the Annual Congress of the European Hematology Association. PTCL is a group of rare and heterogenous malignancies, including ATL, which represent about 10-15% of all non-Hodgkin lymphomas (NHL).3 The majority of patients with PTCL experience disease progression following initial treatment with a multi-drug chemotherapy-based regimen, and median overall survival following relapse is approximately 5.8 months.4 New innovative treatment strategies are needed to improve survival in these patients. In this first-in-human phase 1 study of valemetostat in B-cell and T-cell NHL, data were reported at EHA in the subset of patients with relapsed/refractory PTCL and ATL. The objective response rate (ORR), based on investigators assessment, was 54.5% (CI 95%: 38.8-69.6) in 44 patients with PTCL including 12 complete responses (CRs) and 12 partial responses (PRs). A median duration of response (DOR) of 56.00 weeks (CI 95%: 44.43-NE) and a median progression-free survival (PFS) of 52.00 weeks (CI 95%: 16.14-NE) were observed after a median follow-up of 19.93 weeks (range: 3.1-68.1). The ORR in 14 patients with ATL was 57.1% (CI 95%: 28.9-82.3), with four CRs and four PRs. Median DOR and PFS were not estimable for patients with ATL after a median follow-up of 23.07 weeks (range: 3.3-125.0). Twelve patients with PTCL and six patients with ATL remained on treatment with valemetostat at the time of data cutoff on November 2, 2020. The safety profile of valemetostat in patients with PTCL and ATL (n=58) was similar with that seen across all patients with NHL (n=77). Grade 3 or higher treatment emergent adverse events (TEAEs) occurred in 54 of 77 NHL patients (70.1%) and included neutrophil count decrease (23.4%), lymphocyte count decrease (22.1%), platelet count decrease (16.9%), white blood cell count decrease (15.6%), anemia (11.7%), diarrhea (1.3%) and alanine aminotransferase (ALT) increase (1.3%). Dose interruption or reductions due to TEAEs occurred in 41.6% (n=32) and 10.4% (n=8) of all patients with NHL, respectively. Patients with PTCL enrolled in the study had received a median of two prior treatments (range: 1-8), including prior hematopoietic stem cell transplantation (HSCT; 20.5%). Patients with ATL had received a median of two prior treatments (range: 1-8), including HSCT (14.3%).