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