Phase 1b/2 Study Testing Radium-223 Dichloride/Bortezomib/Dexamethasone Combination in Relapsed Multiple Myeloma

This study will be conducted in 2 parts. The phase 1b part will be an international, phase 1b, open-label, dose-escalation assessment of radium-223 dichloride administered with bortezomib and dexamethasone in subjects with relapsed multiple myeloma. The primary endpoint of the phase 1b part is to determine the optimal dose of radium-223 dichloride in combination with bortezomib/dexamethasone for the Phase 2 portion of the study. The phase 2 part will be an international, phase 2, double-blind, randomized, placebo-controlled assessment of radium-223 dichloride versus placebo administered with bortezomib and dexamethasone, in subjects with relapsed multiple myeloma. Randomization (1:1) in the phase 2 part will be stratified by: * Prior bortezomib treatment (yes, no) * Prior treatment (1 prior line of treatment, \>1 prior line of treatment) Approximately 30 subjects (10 subjects per cohort) will be enrolled in the phase 1b part of the study and approximately 196 subjects will be enrolled in the phase 2 part of the study.