The molecular chaperone heat shock protein 90 (Hsp90) is important in maintaining the conformation, stability, and function of many proteins involved in cell surviving. Hsp90 is of interest as an anticancer drug target because of its importance in maintaining the function of key oncogenic client proteins. Hsp90 inhibitors also have shown promising antitumor activity in vitro and in vivo preclinical model systems. One Hsp90 inhibitor, 17-allylamio-17- desmethoxygeldanamycin (17-AAG), is currently in clinical trial.