This is a phase 3, open label trial for patients with multiple myeloma in first relapse. Trial will compare tanespimycin (KOS-953), in combination with a fixed dose of bortezomib versus bortezomib alone.

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.

Inclusion Criteria:

• Good Performance Status
• Documented evidence of multiple myeloma
• Documented progression of disease after initial response to one line of therapy
• Measurable disease (serum M-protein >.5g/dl or > 200 mg urinary M protein excretion)

Exclusion Criteria:

• Prior treatment with a heat shock 90 inhibitor or an investigational proteasome inhibitor
• Known active infections of HAV, HBV, HCV, or HIV
• Administration of chemotherapy, radiation therapy, or immune therapy within 21 days prior to randomization.
• Acute diffuse infiltrate pulmonary disease or pericardial dise