A Study to Evaluate 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) within 12 months of study entry * 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