Phase 3 combination study comparing tanespimycin (KOS-953) plus bortezomib to bortezomib alone in patients with multiple myeloma in first relapse after failure of previous anti-cancer therapy and/or bone marrow transplantation. Primary objective is to compare the progression-free survival (PFS) associated with the use of tanespimycin (KOS-953) in combination with bortezomib versus that associated with administration of bortezomib alone.