A Study to Learn About the Study Medicine (Elranatamab) in Participants With Multiple Myeloma That Has Come Back After Responding to Treatment or Has Not Responded to Treatment (MagnetisMM-9)

The purpose of this study is to evaluate the safety of a step-up dosing approach (starting with low doses followed by higher doses) of the study medicine (elranatamab) in participants with multiple myeloma that has come back after responding to treatment or has not responded to treatment (relapsed/refractory multiple myeloma). This study will also look at the safety and efficacy of different doses of elranatamab, as well as different intervals between doses.

Inclusion Criteria

1. Diagnosis of multiple myeloma

2. Measurable disease, as defined by at least 1 of the following:
Serum M-protein >0.5 g/dL by SPEP
Urinary M-protein excretion >200 mg/24 hours by UPEP
Serum immunoglobulin FLC≥10 mg/dL (≥100 mg/L) AND abnormal serum immunoglobulin kappa to lambda FLC ratio

3. ECOG performance status ≤1

Exclusion Criteria

1. Smoldering multiple myeloma

2. Active Plasma cell leukemia

3. POEMS syndrome

Study Requirements

Participants in the study will receive elranatamab as an injection under the skin at the study clinic. After the initial step-up doses, participants will start receiving one dose every week. The frequency of clinic visits for injections may then decrease over time. Participation will be at least two years.