A Study of Elranatamab and Cyclophosphamide in People With Multiple Myeloma

Inclusion Criteria: * Documentation of Disease: * Patients must have pathologically confirmed diagnosis of multiple myeloma (MM) as defined according to 2014 IMWG criteria. * Measurable disease defined by at least 1 of the following: * Serum M-protein ≥0.5 g/dL by SPEP * Serum immunoglobulin free light chain ≥10 mg/dL (≥100 mg/L) AND abnormal serum immunoglobulin kappa to lambda free light chain ratio (\<0.26 or \>1.65) * Urinary M-protein excretion ≥200 mg/24 hours by UPEP * Bone marrow plasma cell percentage (in aspirate or biopsy, whichever is higher) of ≥30% * Myeloma bone lesion or plasmacytoma lesion with a single diameter of ≥2 cm * Adverse risk features defined as having ≥1 of the following: * Presence of extramedullary myeloma identifiable by 18F-FDG PET/CT * Serum beta-2-microglobulin (B2M) level ≥5.5 mg/dL * Bone marrow plasma cell percentage (in aspirate or biopsy, whichever is higher) of ≥50% * Prior Treatment Exposure: * Participants have received at least 1 prior lines of therapy for MM including: * At least 1 IMiD (thalidomide, lenalidomide or pomalidomide) * At least 1 PI (bortezomib, carfilzomib or ixazomib) * At least 1 anti-CD38 monoclonal antibody (daratumumab or isatuximab) * Age ≥ 18 * ECOG Performance Status ≤ 2 (See Appendix I for performance status criteria) * Not Pregnant and Not Nursing * The effects of elranatamab and cyclophosphamide on the developing human fetus are unknown. For this reason and because cyclophosphami…