DS-3201b in Participants With Lymphomas

Inclusion Criteria: * Has hematocytological or pathological diagnosis of non- Hodgkin's lymphoma (NHL) * Has relapsed from or is refractory to standard treatment or no standard treatment is available * Is the age of majority in their country (18 in the US and 20 in Japan) at the time of informed consent * Has Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 * Has at least one evaluable lesion site (not applicable for the DDI cohort) * Has preserved organ function based on baseline laboratory data at screening tests * If of reproductive potential, agrees to avoid harvesting ova or sperm, and to use a protocol-defined form of contraception or avoid intercourse, during and upon completion of the study, and for at least 3 months after the last dose of study drug * Tumor biopsy collections: 1. willing to provide archived or fresh tumor tissue samples that are sufficient for comprehensive genomic and/or proteomic analyses at baseline 2. \[US only\] willing to provide fresh on-treatment tumor biopsy if deemed acceptable risk by the investigator \[Japan only\] fresh on-treatment tumor biopsy should be performed if deemed acceptable risk by the investigator 3. willing to provide optional fresh end-of-treatment biopsy For ATL subjects: * Has a positive test result for human T-lymphotropic virus type I antibody * Has ATL subtype classified as acute, lymphomatous, or chronic with poor prognostic factor * Has diagnosis of relapse (including relapse after partial remission \[PR\]) or treatment-resistant ATL at the time of informed consent after prior treatment with at least 1 anti-cancer medication regimen Exclusion Criteria: * Has been diagnosed with protocol-defined cutaneous T-cell lymphoma or T-cell leukemia. For DDI cohort, CTCL is not exclusionary. * Has a history or presence of central nervous system (CNS) involvement * Has a medical history, complication or other malignancy considered inappropriate for participation in the study, or a serious physical or psychiatric disease, the risk of which may be increased by participation in the study * Has received drugs or other treatments not allowed by the protocol * History of treatment with other enhancer of zeste (EZH) inhibitors * Has had allogeneic hematopoietic stem cell transplantation (HTCP) within 90 days before scheduled dosing on Cycle 1 Day 1 * Is pregnant or breastfeeding * Is otherwise deemed ineligible to participate by the investigator or sub-investigator DDI Cohort Only: * Has received following medications within 14 days prior to study drug administration * Any CYP3A inhibitors/inducers including weak CYP3A inhibitors/inducers, and P-gp inhibitors, midazolam as well as digoxin