A Study to Evaluate Change in Disease Activity of Subcutaneous (SC) Epcoritamab Combined With Intravenous and Oral Rituximab, Cyclophosphamide, Doxorubicin Hydrochloride, Vincristine, and Prednisone (R-CHOP) or R-CHOP in Adult Participants With Newly Diagnosed Diffuse Large B-Cell Lymphoma (DLBCL)

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 change in disease activity of epcoritamab when combined with intravenous and oral rituximab, cyclophosphamide, doxorubicin hydrochloride, vincristine, and prednisone (R-CHOP) or R-CHOP in adult participants globally with diffuse large b-cell lymphoma (DLBCL). Change in disease activity will be assessed. Epcoritamab is an investigational drug being developed for the treatment of DLBCL. Study doctors put the participants in groups called treatment arms. Participants will receive epcoritamab combined with R-CHOP, followed by epcoritamab or R-CHOP followed by rituximab will be explored. Approximately 900 adult participants with with newly diagnosed DLBCL will be enrolled in the study in approximately 315 sites in globally. In the Arm 1, participants will receive subcutaneous epcoritamab combined with intravenous and oral R-CHOP followed by subcutaneous epcoritamab in 21-day cycles. In the Arm 2, participants will receive intravenous and oral R-CHOP followed by intravenous rituximab in 21-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.