A trial to determine the safety and effectiveness of CC-92480 in combination with bortezomib and dexamethasone as compared to pomalidomide in combination with bortezomib and dexamethasone in people who have Multiple Myeloma that is not responsive after treatment or has returned after a period of treatment.

Prior treatment

• Subject has had prior treatment with mezigdomide or pomalidomide
• Subject 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.
• 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.

• Subject has documented diagnosis of MM and measurable disease, defined as: —M-protein ≥ 0.5 g/dL by serum protein electrophoresis (sPEP), or ≥ 200 mg/24-hour urine collection by urine protein electrophoresis (uPEP) or —For subjects 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
• Subject has received 1 to 3 prior anti-myeloma lines of therapy
• Subject must have received prior treatment with a lenalidomide containing regimen. For country-specific requirements, see APPENDIX I
• Subject achieved a minimal response [MR] or better to at least 1 prior antimyeloma therapy
• Subject must have documented disease progression during or after their last antimyeloma regimen
• Subject has an Eastern Cooperative Oncology Group (ECOG) performance status score of 0, 1 or 2.