RecruitingDrug trialTesting the Combination of Two Approved Drugs and One Experimental Drug in Patients With Relapsed or Refractory Multiple MyelomaThis phase I/II trial tests the safety, side effects, best dose, and effectiveness of iberdomide in combination with belantamab mafodotin and dexamethasone in treating patients with multiple myeloma (MM) that has come back after a period of improvement (relapsed) or that does not respond to treatment (refractory). Multiple myeloma is a cancer that affects white blood cells called plasma cells, which are made in the bone marrow and are part of the immune system. Multiple myeloma cells have a protein on their surface called B-cell maturation antigen (BCMA) that allows the cancer cells to survive and grow. Immunotherapy with iberdomide, may induce changes in body's immune system and may interfere with the ability of cancer cells to grow and spread. Belantamab mafodotin has been designed to attach to the BCMA protein, which may cause the myeloma cell to become damaged and die. Dexamethasone is in a class of medications called corticosteroids. It is used to reduce inflammation and lower the body's immune response to help lessen the side effects of chemotherapy drugs. Iberdomide plus belantamab mafodotin may help slow or stop the growth of cancer in patients with multiple myeloma.