This study is researching an experimental drug called linvoseltamab, also called REGN5458.

Linvoseltamab has previously been studied by itself (without other cancer drugs) in participants who had advanced multiple myeloma that returned and needed to be treated again after many other therapies had failed. These participants were no longer benefiting from standard medications and had no good treatment options. In that study, some participants who were treated with linvoseltamab had improvement of their myeloma (shrinkage of their tumors), including some participants who had complete responses (that is, the treatment got rid of all evidence of myeloma in their bodies).

This study is focused on participants who have multiple myeloma that has returned or needs to be treated again after one to four prior treatments and have standard cancer treatment options available to them. The aim of this study is to see how safe and effective linvoseltamab is compared to a combination of three cancer drugs: elotuzumab, pomalidomide and dexamethasone, (called EPd) in participants who have returned after having received prior treatment that included lenalidomide, a proteosome inhibitor, and (for participants in some countries) a cluster of differentiation 38 (CD38) antibody. Half of the participants in this study will get linvoseltamab, and the other half will get EPd.

This study is looking at several other research questions, including:

• How long participants benefit from receiving linvoseltamab compared with EPd
• How many participants treated with linvoseltamab or EPd have improvement of their multiple myeloma and by how much
• What side effects happen from taking linvoseltamab compared to EPd
• How long participants live while receiving treatment or after treatment with linvoseltamab compared to EPd
• If there is any improvement in pain after treatment with linvoseltamab compared to EPd

Key Inclusion Criteria:

1. Age 18 years or older (or legal adult age in the country) at the time of the screening visit.

2. Eastern Cooperative Oncology Group (ECOG) performance status ≤1. Patients with ECOG 2 solely due to local symptoms of myeloma (eg. pain) may be allowed after discussion with the Medical Monitor.

3. Received at least 1 and no more than 4 prior lines of anti-neoplastic MM therapies, including lenalidomide and a proteasome inhibitor and demonstrated disease progression on or after the last therapy as defined by the 2016 IMWG criteria. Participants who have received only 1 line of prior line of antimyeloma therapy must be lenalidomide refractory, as described in the protocol.

   Note: Participants in Israel also must have previously received a CD38 antibody. Participants in the EU and the UK must have previously received 2 to 4 prior lines of therapy, including a CD38 antibody.

4. Patients must have measurable disease for response assessment as per the 2016 IMWG response assessment criteria, as described in the protocol

5. Adequate hematologic function and hepatic function within 7 days of randomization, as well as adequate renal and cardiac function and corrected calcium

6. Life expectancy of at least 6 months

Key Exclusion Criteria:

1. Diagnosis of plasma cell leukemia, amyloidosis, Waldenström macroglobulinemia, or POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes).
2. Prior treatment with elotuzumab and/or pomalidomide
3. Participants with known MM brain lesions or meningeal involvement
4. Treatment with any systemic anti-cancer therapy within 5 half-lives or within 28 days before first administration of study drug, whichever is shorter
5. History of allogeneic stem cell transplantation within 6 months, or autologous stem cell transplantation within 12 weeks of the start of study treatment. Participants who have received an allogeneic transplant must be off all immunosuppressive medications for 6 weeks without signs of graft-versus-host disease. Steroids at doses equivalent to suppletion doses may be acceptable.
6. Prior treatment with B-cell maturation antigen (BCMA) directed immunotherapies Note: BCMA antibody-drug conjugates are allowed.
7. History of progressive multifocal leukoencephalopathy (PML), known or suspected PML, or history of a neurocognitive condition or central nervous system (CNS) movement disorder (Parkinson's disease or Parkinsonism).
8. Any infection requiring hospitalization or treatment with IV anti-infectives within 2 weeks of first administration of study drug
9. Uncontrolled infection with human immunodeficiency virus (HIV), hepatitis B virus (HBV) or hepatitis C virus (HCV); or another uncontrolled infection, as defined in the protocol 10 Cardiac ejection fraction <40%.

NOTE: Other protocol defined inclusion/exclusion criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf