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

Inclusion Criteria

• •At least one bi-dimensionally measurable nodal lesion, defined as \> 1.5 cm in its longest dimension, or one bi-dimensionally measurable extranodal lesion, defined as \> 1.0 cm in its longest diameter
• •Adequate hematologic function
• •Eastern Cooperative Oncology Group (ECOG) Performance Status of 0, 1, or 2; with the exception of South Korea, where participants 80 years or older with ECOG \>/= 2 will not be eligible
• •Participants in Cohort A must also meet the following criteria for study entry:
• •Histologically confirmed DLBCL according to World Health Organization (WHO) 2016 expected to express the cluster of differentiation-20 (CD20) antigen
• •One prior therapy with any systemic anthracycline-based chemoimmunotherapy containing regimen for previously untreated DLBCL
• •Best response of SD or PR to prior systemic chemoimmunotherapy at the end of induction treatment in accordance with the Lugano 2014 criteria
• •Participants in Cohorts B and C must also meet the following criteria for study entry:
• •Previously untreated, histologically confirmed, DLBCL according to WHO 2016 classification
• •Age \>/= 80 years, or
• •Age 65-79 years and considered ineligible for chemoimmuotherapy (R-CHOP) with at least one of the following: Impairment in at least two activity of daily living (ADL) components as defined in the protocol; impairment in at least two instrumental ADL components as defined in the protocol; cumulative illness rating scale - geriactic (CIRS-G) score of at least one cormorbidity with a severity score of 3-4 (not including lymphoma and hematologic deficiencies due to lymphoma) or a score of 2 in \>/= 8 comorbidities; impairment in cardiac function, renal function, liver function, or other comorbidities such that the participant is unfit for full-dose immunochemotherapy, such as rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP)
• •Participants 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 (not more than 100 mg/day up to 7 days prior to Cycle 1 Day 1) results in an improvement of ECOG performance status to \</= 2 prior to enrollment