A Phase 2, Multicentre, Randomised, Open-Label, Parallel Group Study to Evaluate the Safety and Efficacy of VELCADE in combination with Dexamethasone or VELCADE in Combination with Dexamethasone and Cyclophosphomide or VELCADE in combination with Dexamethasone and Lenalidomide ind Subjects with Multiple Myeloma who are Refractory to or Have Relapsed / progressed after Primary Therapy for Multiple Myeloma and have achieved stable disease after 4 cycles of VELCADE/Dexamethasone therapy