This is a phase 2/3, open label trial for patients with relapsed-refractory multiple myeloma. Study agent is tanespimycin (KOS-953), at three different dose levels in combination with a fixed dose of bortezomib.

Phase 2/3 combination study comparing bortezomib plus one of three doses of tanespimycin in patients with relapsed-refractory multiple myeloma after failure of at least three prior anti-cancer therapy regimens. Prior therapy must include bortezomib and lenalidomide. Primary objective is to assess the dose-response relationship of objective response rate (ORR) using EBMT/IBMTR criteria of any three dose levels of tanespimycin (KOS-953) in combination with bortezomib after four treatment cycles.

Inclusion Criteria:

• Good performance status
• Histologic evidence of multiple myeloma
• Have had at least three prior treatment regimens for multiple myeloma that included both bortezomib and lenalidomide
• No prior treatment with a heat shock 90 inhibitor or an investigational proteasome inhibitor
• No known infections of HAV, HBV, HCV, or HIV
• No chemotherapy, radiation therapy, or immune therapy for three weeks prior to enrollment.