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

Inclusion Criteria:

Participant has documented diagnosis of MM and measurable disease, defined as any of the following:

1. M-protein ≥ 0.5 grams per deciliter (g/dL) by serum protein electrophoresis (sPEP) or
2. M-protein ≥ 200 milligrams (mg) per 24-hour urine collection by urine protein electrophoresis (uPEP)
3. 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.
4. Participants received 1 to 3 prior lines of antimyeloma therapy.
5. 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:

a. Subjects who progressed while being treated with, or within 60 days of last dose of bortezomib maintenance given once every 2 weeks or less are not excluded.

1. 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.
2. Participant has had prior treatment with mezigdomide or pomalidomide.

Other protocol-defined criteria apply.