A Study to Evaluate Adverse Events and Change in Disease Activity of Subcutaneous (SC) Epcoritamab As Monotherapy or Combined With Standard of Care Therapies in Adult Participants in China With B-Cell Non-Hodgkin Lymphoma

B-cell Lymphoma is an aggressive and rare cancer of a type of immune cells (a white blood cell responsible for fighting infections). The purpose of this study is to assess the safety and toxicity of epcoritamab as a monotherapy and when combined with standard of care therapy \[Rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) or Rituximab and lenalidomide (R2)\] in adult participants in China with B-Cell Non-Hodgkin Lymphoma. Adverse events and change in disease activity will be assessed. Epcoritamab is an investigational drug being developed for the treatment of B-Cell Non-Hodgkin Lymphoma. Study doctors put the participants in groups called treatment arms. A monotherapy of epcoritamab and two different combination of epcoritamab with standard of care therapy (R-CHOP or R2) will be explored. Each treatment arm receives a different treatment combination depending on stage of the study and eligibility. Approximately 66 adult participants with B-Cell Non-Hodgkin Lymphoma will be enrolled in the study in approximately 21 sites in China. In the monotherapy arm (Cohort 1), participants will receive subcutaneous epcoritamab in 28-day cycles. In the combination arms (Cohorts 2 and 3), participants in Cohort 2 will receive subcutaneous epcoritamab with standard of care therapy (R-CHOP) in 21-day cycles followed by 28-day cycles, participants in Cohort 3 will receive subcutaneous epcoritamab with standard of care therapy (R2) in 28-day cycles. There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at an approved institution (hospital or clinic). The effect of the treatment will be frequently checked by medical assessments, blood tests, questionnaires and side effects.