The purpose of this study is to compare the efficacy and safety of mezigdomide (CC-92480), bortezomib and dexamethasone (MeziVd) versus pomalidomide, bortezomib and dexamethasone (PVd) in participants with relapsed or refractory multiple myeloma (RRMM) who received between 1 to 3 prior lines of therapy and who have had prior lenalidomide exposure.
Participants received 1 to 3 prior lines of antimyeloma therapy.
Participants achieved minimal response [MR] or better to at least 1 prior antimyeloma therapy.
For participants with prior treatment of a bortezomib containing regimen, the best response achieved was not a minimal response (MR) or better, or participant discontinued bortezomib due to toxicity.
Participant has had prior treatment with mezigdomide or pomalidomide.
Other protocol-defined Inclusion/Exclusion criteria apply.