This study looks at new medicine combinations to treat relapsed or refractory multiple myeloma (RRMM), a blood cancer that comes back or doesn't respond to treatment. It involves using a new drug called Mezigdomide with two known drugs, Carfilzomib and Dexamethasone. The study compares this new combination (MeziKD) to the usual two-drug combo (Kd) to see which works better. Participants must have had at least one previous treatment for multiple myeloma, and their disease must have gotten worse after their last treatment. They can't join if they've used Mezigdomide or Carfilzomib before or had certain types of stem cell transplants recently. To join, participants need certain levels of a protein called M-protein, which can be found in the blood or urine, or have high levels of light chains, proteins involved in multiple myeloma.

• Study involves comparing two drug combinations for effectiveness.
• Participants must have tried at least one previous treatment.
• Must not have used some specific treatments before joining.