• Provision of signed and dated informed consent form

• Stated willingness to comply with all study procedures and availability for the duration of the study

• Prior diagnosis of relapsed/refractory MM and have received 1 to 3 prior lines of therapy as defined by the IMWG criteria (Rajkumar et al., 2014) including anti-CD38 monoclonal antibody, proteosome inhibitor (PI), and immunomodulatory drug (IMiD), and BCMA-directed chimeric antigen receptor T-cell (CAR T-cell) therapy

∙ Refractory is defined as having disease progression while on therapy or within 60 days of last dose in any line, regardless of response.

‣ If participant has not received BCMA-directed CAR T-cell therapy, must be ineligible for CAR T-cell therapy or deferred such treatment by participant

• Aged greater or equal to 18 years

• Measurable disease as defined by any of the following:

∙ Serum M-protein level ≥ 0.5 g/dL by serum protein electrophoresis (SPEP), or

‣ Urine M-protein ≥ 200mg/24 hours by urine protein electrophoresis (UPEP), or

‣ Involved serum free light chain ≥ 10 mg/dL (≥100mg/L) AND an abnormal serum free light chain ratio in patients without measurable disease in the serum or urine

• Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2

• Adequate hematological function defined as

∙ Absolute neutrophil count (ANC) ≥1,000/mm3 (G-CSF not permitted for at least 1 week prior to the first dose of elranatamab)

‣ Hemoglobin ≥8.0 g/dL (transfusion support is permitted if completed at least 1 week prior to planned start of dosing)

‣ Platelet count ≥75,000/mm3 or ≥50,000/mm3 if \>50% involvement with plasma cells in the screening bone marrow (transfusion support is permitted if completed at least 1 week prior to planned start of dosing)

• Adequate renal function with estimated creatinine clearance (CrCl) ≥30 mL/min as calculated using Cockcroft-Gault equation.

• Adequate liver function defined as

∙ Aspartate and alanine aminotransferase (AST and ALT) ≤2.5 x upper limit of normal (ULN); ≤5.0 x ULN if there is liver involvement by the tumor.

‣ Alkaline phosphatase ≤2.5 x ULN (≤5 x ULN in case of bone metastasis).

‣ Total bilirubin ≤2.0 mg/dL, except in patients with Gilbert Syndrome who must have a total bilirubin less than 3.0 mg/dL.

⁃ Able to receive outpatient treatment of elranatamab by meeting the following criteria:

• Lives within 30minutes from the site of medication administration

∙ Reliable caregiver present, who is able to watch participant continuously for at least until 48 hours after administration of first full treatment dose

∙ No history of grade 3-4 CRS or grade 3-4 ICANS from other immune effector cell or bispecific antibody therapies

⁃ Resolved acute effects of any prior therapy to baseline severity or CTCAE Grade ≤1

⁃ Serum pregnancy test (for females of childbearing potential) negative at screening.

⁃ a. Female patients of non-childbearing potential must meet at least 1 of the following criteria: i. Achieved postmenopausal status, defined as follows: cessation of regular menses for at least 12 consecutive months with no alternative pathological or physiological cause; status may be confirmed with a serum follicle stimulating hormone (FSH) level confirming the postmenopausal state.

⁃ ii. Have undergone a documented hysterectomy and/or bilateral oophorectomy. iii. Have medically confirmed ovarian failure. b. All other female patients (including female patients with tubal ligations) are considered to be of childbearing potential.

⁃ Agreement to adhere to Lifestyle Considerations (see section 5.3 and Appendix 2) throughout study duration