Multiple myeloma is a cancer of plasma cells that remains largely incurable. While initial treatments can achieve remission, patients will typically relapse with fewer treatment options available. Current therapies for relapsed and refractory multiple myeloma have limited efficacy and serious side effects. There remains an unmet need for additional effective and tolerable treatments. Carfilzomib is a novel proteasome inhibitor that has shown clinical activity with durable responses and an acceptable safety profile in patients with relapsed and refractory multiple myeloma who have limited treatment options.