Valemetostat Tosylate (DS-3201b), an Enhancer of Zeste Homolog (EZH) 1/2 Dual Inhibitor, for Relapsed/Refractory Peripheral T-Cell Lymphoma (VALENTINE-PTCL01)

Inclusion Criteria: * Written informed consent * Participants ≥18 years of age or the minimum legal adult age (whichever is greater) at the time the informed consent form is signed. * Eastern Cooperative Oncology Group performance status of 0, 1, or 2 * Cohort 1 relapsed/refractory peripheral T-cell lymphoma (PTCL): * Diagnosis should be confirmed by the local pathologist; local histological diagnosis will be used for eligibility determination. Participants with the following subtypes of PTCL are eligible according to 2016 WHO classification prior to the initiation of study drug. Any T-cell lymphoid malignancies not listed are excluded. Eligible subtypes include: * Enteropathy-associated T-cell lymphoma * Monomorphic epitheliotropic intestinal T-cell lymphoma * Hepatosplenic T-cell lymphoma * Primary cutaneous γδ T-cell lymphoma * Primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma * PTCL, not otherwise specified * Angioimmunoblastic T-cell lymphoma * Follicular T-cell lymphoma * Nodal PTCL with T-follicular helper (TFH) phenotype * Anaplastic large cell lymphoma, ALK positive * Anaplastic large cell lymphoma, ALK negative * Cohort 2 relapsed/refractory adult T-cell leukemia/lymphoma (ATL) acute, lymphoma, or unfavorable chronic type. Relapsed/refractory ATL should be confirmed by the local pathologist; local diagnosis will be used for eligibility determination. The positivity of anti-human T-cell leukemi…