A Study to Evaluate Mezigdomide, Bortezomib and Dexamethasone (MEZIVd) Versus Pomalidomide, Bortezomib and Dexamethasone (PVd) in Participants With Relapsed or Refractory Multiple Myeloma (RRMM)

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.

Inclusion Criteria \- Participant has documented diagnosis of MM and measurable disease, defined as any of the following:. i) M-protein ≥ 0.5 grams per deciliter (g/dL) by serum protein electrophoresis (sPEP) or. ii) M-protein ≥ 200 milligrams (mg) per 24-hour urine collection by urine protein electrophoresis (uPEP). iii) For participants without measurable disease in sPEP or uPEP: serum free light chain (sFLC) levels \> 100 mg/L (10 mg/dL) involved light chain and an abnormal kappa/lambda FLC ratio. * Participants received 1 to 3 prior lines of antimyeloma therapy. * Participants achieved minimal response \[MR\] or better to at least 1 prior antimyeloma therapy. Exclusion Criteria \- Participant has had progression during treatment or within 60 days of the last dose of a proteasome inhibitor, except as noted below:. i) Subjects who progressed while being treated with, or within 60 days of last dose of bortezomib maintenance given once every 2 weeks (or less frequently) are not excluded. ii) Participants who progressed while being treated with ixazomib monotherapy maintenance ≥ 6 months prior to the time of starting study treatment are not excluded. * 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.