Filanesib is a highly selective, targeted KSP inhibitor with a mechanism of action distinct from currently available myeloma therapies such as immunomodulatory drugs (IMiDs®) and proteasome inhibitors. Across multiple studies, filanesib has demonstrated activity in heavily pretreated multiple myeloma patients, with a consistent safety profile including no drug-induced peripheral neuropathy and limited non-hematologic toxicity. Adverse events are generally limited to transient, non-cumulative and predominantly asymptomatic myelosuppression (decreases in blood counts) when supportive measures are used. Alpha 1-acid glycoprotein (AAG), a plasma protein, is a potential patient selection marker for filanesib. AAG is undergoing further investigation in clinical trials and could represent the first patient selection marker for a myeloma therapy. Filanesib is in Phase II for Multiple myeloma treatment.