Glofitamab With Pirtobrutinib for Relapsed or Refractory Mantle Cell Lymphoma

This phase II trial tests the safety and effectiveness of glofitamab given in combination with pirtobrutinib in treating patients with mantle cell lymphoma that has come back after a period of improvement (relapsed) or that has not responded to previous treatment (refractory). Glofitamab and obinutuzumab are monoclonal antibodies that may interfere with the ability of cancer cells to grow and spread. Obinutuzumab may also reduce the risk of immune-related conditions from treatment. Pirtobrutinib is in a class of medications called kinase inhibitors. It works by blocking the action of the protein that signals cancer cells to multiply. Giving glofitamab in combination with pirtobrutinib may be safe, tolerable and/or effective in treating patients with relapsed or refractory mantle cell lymphoma.

Inclusion Criteria: * Age ≥ 18 years at the time of signing the informed consent form. * Have a life expectancy (in the opinion of the investigator) of at least 12 weeks. * Eastern Cooperative Oncology Group (ECOG) performance status \< 2 (Karnofsky \> 60%). * History of previously treated MCL meeting the following criteria: Relapsed after or failed to respond to at least one prior line of systemic therapy including anti-CD20 monoclonal antibody and alkylator-containing chemotherapy. * At least one bi-dimensionally measurable nodal lesion ( \> 1.5 cm in its largest dimension by PET/CT scan), or at least one bi-dimensionally measurable extranodal lesion ( \> 1.0 cm in its largest dimension by PET/CT scan) and FDG-avid. * Availability of leftover tissue from the time of progression for pathology confirmation and correlative studies. Note: Formalin fixed paraffin embedded blocks are preferred. If blocks are not available, 12-15 slides containing unstained, serial sections are acceptable. * Hemoglobin ≥ 9 g/dL (Independent of transfusions and within 7 days prior to screening assessment). * Absolute neutrophil count \>= 1.0 x 10\^9/L (Independent of growth factor support and within 7 days prior to screening assessment). * Platelets ≥ 75 x 10\^9/L or \>= 50 x 10\^9/L if due to bone marrow involvement (Independent of transfusions and within 7 days prior to screening assessment, and independent of growth factor support and within 7 days prior to screening assessment). If the patient is cytopenic there should be no evidence of myelodysplasia orhypoplastic bone marrow. * Total bilirubin ≤ 1.5 x upper limit of normal (ULN) (or ≤ 3 x ULN for participants with Gilbert syndrome, or \