Trial of Mosunetuzumab (BTCT4465A) as Consolidation Therapy in Participants With Diffuse Large B-Cell Lymphoma Following First-Line Immunochemotherapy and as Monotherapy or in Combination With Polatuzumab Vedotin in Elderly/ Unfit Participants With Previously Untreated Diffuse Large B-Cell Lymphoma

Prior treatment

• For All Cohorts Prior treatment with mosunetuzumab
• Cohort A Prior anti-lymphoma treatment with chemotherapy, immunotherapy, or biologic therapy within 4 weeks prior to C1D1
• Cohorts B and C Prior treatment for DLBCL with chemotherapy, immunotherapy, and biologic therapy Exception: patients in Cohort B who are treated with vincristine and prednisone as part of pre-phase treatment or patients in Cohort C who are treated with prednisone as part of pre-phase treatment

Other illness

• For All Cohorts History of confirmed progressive multifocal leukoencephalopathy (PML)
• Cohort C Current Grade >1 peripheral neuropathy by clinical examination or demyelinating form of Charcot-Marie-Tooth disease

Other

• For All Cohorts Transformed lymphoma, CNS lymphoma

• For All Cohorts At least one bi-dimensionally measurable nodal (>1.5cm) lesion or extranodal (>1.0 Cm) lesion
• For All Cohorts Eastern Cooperative Oncology Group (ECOG) Performance Status of 0, 1, or 2. Exception (Cohort C only): in South Korea, patients 80 years or older with ECOG >=2, will not be eligible
• Cohort A One prior therapy with any systemic anthracycline based chemoimmunotherapy containing regimen for previously untreated DLBCL and Best response of SD or PR to prior systemic chemoimmunotherapy at the end of the induction treatment in accordance with the Lugano 2014 criteria
• Cohort C Age >= 80 years or Patients who are 65−79 years of age, and considered ineligible for chemoimmunotherapy (R CHOP) at least one of the following: Impairment in >= 2 ADL component and/or Impairment in >= 2 instrumental ADL (IADL) component and/or CIRS-G score of at least 1 comorbidity with a severity score of 3-4 (not including lymphoma and hematologic deficiencies due to lymphoma) or a score of 2 in >=8 comorbidities
• Cohorts B and C Patients with an initial ECOG performance status of 3 may be considered during screening if the performance status is DLBCL-related and if pre-phase treatment during the screening phase results in an improvement of ECOG performance status to <=2 prior to enrollment
• Cohort B ≥ 80 years of age, or 60-79 years of age and unfit for full-dose chemotherapy because of poor performance status, impairments in ADL or instrumental activities of daily living (IADL), or other comorbidities