MagnetisMM-32: A Study to Learn About the Study Medicine Called Elranatamab in People With Multiple Myeloma (MM) That Has Come Back After Taking Other Treatments (Including Prior Treatment With an Anti-CD38 Antibody and Lenalidomide)

Inclusion Criteria: * Prior diagnosis of multiple myeloma as defined by International Myeloma Working Group (IMWG) criteria and previously received 1 to 4 prior lines of therapy including prior anti-cluster of differentiation 38 (CD38) antibody and prior lenalidomide. * Documented evidence of progressive disease or failure to achieve a response to last line of therapy per IMWG criteria. * Measurable disease defined as at least 1 of the following: (a) Serum M-protein ≥0.5 g/dL; (b) Urinary M-protein excretion ≥200 mg/24 hours; (c) Serum involved immunoglobulin FLC ≥10 mg/dL AND abnormal serum immunoglobulin kappa to lambda FLC ratio (\<0.26 or \>1.65). * Have clinical laboratory values within the specified range. * ECOG (Eastern Cooperative Oncology Group) performance status ≤2. * Not pregnant or breastfeeding and willing to use contraception. Exclusion Criteria: * Smoldering multiple myeloma. * Plasma cell leukemia. * Amyloidosis. * Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy and skin abnormalities (POEMS) syndrome. * Known central nervous system (CNS) involvement or clinical signs of myelomatous meningeal involvement. * Stem cell transplant within 12 weeks prior to enrolment, or active graft versus host disease. * Any active, uncontrolled bacterial, fungal, or viral infection. * Any other active malignancy within 3 years prior to enrolment (exceptions include, adequately treated basal cell or squamous cell skin cancer, carcinoma in situ) * Previous treatment with a B cell maturation antigen (BCMA)-directed therapy or CD3-redirecting therapy. * Unable to receive investigator's choice therapy. * Live attenuated vaccine within 4 weeks of the first dose of study intervention. * Administration with an investigational product (e.g. drug or vaccine) within 30 days preceding the first dose of study intervention used in this study.