This clinical trial is focused on studying a disease called Multiple Myeloma, which is a type of cancer that affects plasma cells in the bone marrow. The study is testing a new treatment called Linvoseltamab, also known by its code name REGN5458. Linvoseltamab is a special type of medication known as a bispecific antibody, which is designed to target and attack cancer cells. The trial will also use another medication called Dexamethasone, which is a corticosteroid that helps reduce inflammation and can support cancer treatment.

The purpose of this study is to learn if Linvoseltamab is safe and well-tolerated, and to see how well it works in people who have recently been diagnosed with Multiple Myeloma and have not yet received treatment. The study is divided into two phases. In the first phase, researchers will focus on understanding the safety and best dose of Linvoseltamab. In the second phase, they will look at how effective the treatment is in reducing the cancer in patients who are eligible for high-dose chemotherapy and stem cell transplantation, as well as those who are not eligible for these procedures.

Participants in the study will receive Linvoseltamab either through an injection or infusion, and Dexamethasone will be given in tablet form or as an injection. The study will last for a period of up to two years, during which time participants will be closely monitored for any side effects and to assess how well the treatment is working. The goal is to find out if Linvoseltamab can help improve the condition of patients with Multiple Myeloma and to gather important information that could lead to new treatment options in the future.