In the past decade, immunomodulatory drugs have been approved by the US Food and 
Drug Administration for the treatment of multiple myeloma (MM)-and a number of 
emerging agents that target the cellular pathways or proteins involved in the 
pathophysiology of MM are currently in development. Lenalidomide (Revlimid) and 
pomalidomide induce apoptosis and sensitize MM cells while demonstrating 
superior efficacy and better tolerability than thalidomide (Thalomid). Several 
novel classes of drugs, including the histone deacetylase (HDAC) inhibitors, 
heat shock protein (HSP) inhibitors, and monoclonal antibodies have been shown 
to have activity in myeloma in early-stage clinical trials. HDAC inhibitors, 
including vorinostat (Zolinza), panobinostat, and romidepsin (Istodax) are 
thought to affect multiple pathways involved in MM and correct the deregulation 
of genes involved in apoptosis and cell cycle arrest, thus potentially 
sensitizing MM cells to apoptosis. HSP inhibitors (eg, tanespimycin) decrease MM 
proliferation and suppress the long-term replicative potential of MM cells; they 
may also sensitize MM cells to other anticancer agents. The humanized monoclonal 
antibody elotuzumab induces antibody-dependent cell cytotoxicity-mediated 
apoptosis. It is likely that in the near future the treatment armamentarium for 
MM will undergo significant expansion as some of these additional target 
pathways become validated.