Relapsed Andor Refractory Multiple Myeloma Rrmm

This study is researching a drug called linvoseltamab (also called "study drug") either given alone or in combination with another anti-myeloma drug called carfilzomib, compared to several standard treatments for progressive Multiple Myeloma (MM) after at least 1 but no more than 3 prior therapies. The aim of this study is to see if the safety and efficacy of linvoseltamab alone or in combination with carfilzomib can deliver better outcomes (deeper and longer responses that help extend life) than standard treatment options. The study is looking at several other research questions, including: * What side effects may happen from taking the study drug * How much study drug is in the blood at different times * Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects)

Background: Multiple myeloma (MM) is an incurable cancer of certain blood cells. MM often returns after treatment, and most people survive only 5 to 8 years after diagnosis. To improve survival, researchers need to find ways to identify returning disease earlier. Objective: To find out if the radiotracer 18F-fluciclovine (a substance injected into the blood during imaging scans) is better at detecting MM than the one (18F-FDG) currently used for this purpose. Eligibility: Adults aged 18 years or older with MM. The MM may be newly diagnosed (NDMM); or it may have returned or failed to respond after at least 1 prior line of treatment (RRMM). Design: Participants will be screened. They will have blood tests. They will have a positron emission tomography (PET) or computed tomography (CT) scan using 18F-FDG. The radiotracer will be injected into a vein. Then participants will lie on a table while the PET/CT scan takes images of their body. All participants will have 3 study visits. During each visit they will have: Two PET/CT scans. One with 18F-FDG, one with 18F-fluciclovine. An optional magnetic resonance imaging scan. A bone marrow biopsy. An area on the hip will be numbed; a needle will be inserted to draw out a sample of the soft tissue from inside the bone. These tests may be spread over 30 days for each visit. NDMM participants will have their second study visit 2 to 4 weeks after they complete their usual treatment for the disease. RRMM participants will have their second visit 6 months after their first. All participants will have a third study visit after 5 years or when their disease progresses.