Trial of the Safety and Efficacy of Epcoritamab in Japanese Subjects With Relapsed or Refractory (R/R) B-Cell Non-Hodgkin Lymphoma (R/R B-NHL)

Main Inclusion Criteria: • Must be at least 20 years of age, inclusive • Japanese participants • CD20 positivity at representative tumor biopsy 1. Part 1: * Diffuse large B-cell lymphoma (de novo or histologically transformed) * High-grade B-cell lymphoma * Primary mediastinal large B-cell lymphoma * Follicular lymphoma * Marginal zone lymphoma (nodal, extranodal of mucosa-associated lymphoid tissue, or splenic) * Small lymphocytic lymphoma 2. Part 2 : Arm 1: * Diffuse large B-cell lymphoma (de novo or histologically transformed) * Follicular lymphoma grade 1-3A * Relapsed or refractory disease and previously treated with at least 2 lines of systemic antineoplastic therapy including at least 1 anti-CD20 monoclonal antibody (mAb)-containing therapy. * Measurable disease by computed tomography (CT), magnetic resonance imaging (MRI) or positron emission tomography (PET)-CT scan Arm 2: • R/R FL grade 1, 2 or 3a, stage II, III, or IV, without evidence of transformation. * Previously treated with at least 1 prior anti-neoplastic agent, including anti-CD20 antibody * Must have a need for treatment initiation based on symptoms and/or disease burden (Groupe d'Etude des Lymphomes Folliculaires \[GELF\] criteria) * Eligible to receive R2 per investigator determination Arm 3: * One of following confirmed histologies (de novo or histologically transformed from FL or nodal marginal zone lymphoma) : o DLBCL, not otherwise specified (NOS) * "Double-hit" or "triple-hit" DLBCL * FL Grade 3B. * T-cell/histiocyte rich large B-cell lymphoma (LBCL) * International Prognostic Index (IPI) score ≥3 * No prior therapy for DLBCL or FL grade 3B (G3B) other than nodal biopsy, corticosteroids, or palliative radiotherapy. * Eligible to receive R-CHOP per investigator determination Arm 4: * One of following confirmed histologies (de novo or histologically transformed from FL or nodal marginal zone lymphoma) including: o DLBCL, NOS. o "Double-hit" or "triple-hit" DLBCL * FL Grade 3B. * T-cell/histiocyte rich LBCL * Relapsed or refractory to at least one prior therapy including at least one prior anti-CD20 antibody. * Either failed prior autologous hematopoietic stem cell transplantation (ASCT), or ineligible for autologous hematopoietic stem-cell transplantation (HSCT) * Eligible to receive GemOx per investigator determination Arm 5: • History of histologically confirmed CD20+ FL Grade 1-3a without evidence of transformation. • In CR or PR per Lugano criteria following first-line or second-line treatment with SOC regimen, including anti-CD20 antibody, and last dose of SOC within 6 months prior to enrollment Main Exclusion Criteria: • Primary central nervous system (CNS) lymphoma or CNS involvement by lymphoma at screening • Participants not eligible for high dose therapy with autologous hematopoietic stem cell transplantation due to personal choice, social issues, or similar • Known clinically significant cardiac disease • Chronic ongoing infectious diseases requiring treatment (excluding prophylactic treatment) Exclusion criteria for Part 2, Arms 2 through 5: Arm 2: • FL Grade 3b • Histologic evidence of transformation to an aggressive lymphoma * Contraindication to rituximab or lenalidomide * Unwilling or unable to take aspirin prophylaxis or prophylactic anticoagulant as clinically indicated Arm 3: • Contraindication to any of the individual drugs of the R-CHOP regimen Arm 4: * Contraindication to any of the individual drugs of the GemOx regimen Arm 5: * FL Grade 3b * Histologic evidence of transformation to an aggressive lymphoma