Bortezomib (VELCADE®) is an intravenously administered reversible, selective inhibitor of the 26S proteosome. Although all of the mechanisms by which this novel drug acts as an antineoplastic agent are not fully understood, in vivo and in vitro studies indicate they ultimately result in the inhibition of the gene expression necessary for cell growth and survival pathways, apoptotic pathways, and cellular adhesion, migration, and angiogenesis mechanisms.