The future of therapy for relapsed/refractory multiple myeloma: emerging agents and novel treatment strategies.

Treatment of relapsed or refractory multiple myeloma (MM) continues to present a therapeutic challenge. The immunomodulatory drugs (IMiDs) thalidomide and lenalidomide, and the proteasome inhibitor (PI) bortezomib, have dramatically improved clinical outcomes for patients with newly diagnosed and relapsed/refractory MM. However, nearly all patients will eventually relapse or become refractory to these drugs. Numerous agents are currently in development for the treatment of relapsed/refractory MM. Those farthest along in clinical development include new IMiDs (pomalidomide), new PIs (eg, carfilzomib, MLN9708, and marizomib), histone deacetylase inhibitors (eg, panobinostat and vorinostat), monoclonal antibodies (eg, elotuzumab, siltuximab, and BT062), and signal transduction modulators (eg, perifosine). These emerging agents with diverse mechanisms of action have demonstrated promising anti-tumor activity in patients with relapsed/refractory MM, and rationally designed combinations with established agents are being investigated in the clinic. These new agents are creating opportunities to target multiple pathways, overcome resistance, and improve clinical outcomes, particularly for those patients who are refractory to approved novel agents. This article describes emerging antimyeloma agents in mid-stage to late-stage clinical development, and highlights the novel treatment approaches and combination strategies being evaluated in the relapsed/refractory setting.