A Phase III, Open-Label, Multicenter, Randomized Study Evaluating Glofitamab as a Single Agent vs. Investigator's Choice in Participants With Relapsed/Refractory Mantle Cell Lymphoma.

Inclusion Criteria: - Life expectancy at least 12 weeks - Histologically-confirmed MCL, with documentation of either overexpression of cyclin D1 or the presence of t(11:14) - Relapsed (disease progression after the last treatment regimen) or refractory (failure to achieve a partial or complete response from the last treatment regimen) disease - At least 1 line of prior systemic therapy including a BTK inhibitor and additional systemic therapy option - Confirmed availability of tumor tissue, unless deemed unsafe per investigator assessment - At least one bi-dimensionally measurable (defined as at least 1.5 cm) nodal lesion, or one bi-dimensionally measurable (at least 1 cm) extranodal lesion, as measured on CT scan - Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2 - Negative HIV test at screening - Adequate hematological function Exclusion Criteria: - Pregnancy or breastfeeding, or intention of becoming pregnant during the study or within 3 months after the final dose of tocilizumab, 2 months after the final dose of glofitamab, whichever is longer - Leukemic, non-nodal MCL - History of severe allergic or anaphylactic reactions to humanized or murine monoclonal antibodies (or recombinant antibody-related fusion proteins) or known sensitivity or allergy to murine products - Contraindication to obinutuzumab or rituximab, and either bendamustine or lenalidomide - Prior treatment with glofitamab or other bispecific antibodies targeting both CD20 and CD3 - Prior treatment with CAR-T cell therapy - Treatment with systemic therapy or BTK inhibitors, or any investigational agent for the purposes of treating cancer within 2 weeks or 5 half-lives (whichever is shorter) prior to first study treatment - Primary or secondary CNS lymphoma at the time of recruitment or history of CNS lymphoma - Current or history of CNS disease, such as stroke, epilepisy, CNS vasculitis, or neurodegenerative disease - History of other malignancy that could affect compliance with the protocol or interpretation of results - Significant or extensive cardiovascular disease - Known active bacterial, viral, fungal, mycobacterial, parasitic, or other infection at study enrollment or any major episode of infection within 4 weeks prior to the first study treatment - Suspected or latent tuberculosis - Positive test for hepatitis B virus (HBV) or hepatitis C virus (HCV) - Known or suspected chronic active Epstein-Barr viral infection (EBV) - Known or suspected history of hemophagocytic lymphohistiocytosis (HLH) - Known history of progressive multifocal leukoencephalopathy (PML) - Adverse events from prior anti-cancer therapy that have not resolved to Grade 1 or better - Administration of a live, attenuated vaccine within 4 weeks before first study treatment administration or anticipation that such a live, attenuated vaccine will be required during the study - Prior solid organ transplantation or allogenic stem cell transplant - Eligibility for stem cell transplantation (SCT) - Active autoimmune disease requiring treatment - Prior treatment with systemic immunosuppressive medications within 2 weeks or five half-lives (whichever is shorter) prior to the first dose of study treatment - Corticosteroid therapy within 2 weeks prior to first dose of study treatment - Recent major surgery (within 4 weeks before the first study treatment) other than for diagnosis - Clinically significant history of cirrhotic liver disease