Hsp90 controls the proper folding, function, and stability of various "client" proteins within cells. Many of the clients of Hsp90 (such as Akt, Bcr-Abl, EGFR, Flt-3, c-Kit and PDGFR α) are oncoproteins or important cell-signaling proteins, and therefore are critical for tumor cell growth and survival. Inhibition of Hsp90 results in degradation of these proteins, which abrogates growth and survival signaling and leads to tumor cell death.