17-allylamino-17-demethoxygeldanamycin (17-AAG) was the first Hsp90 inhibitor which entered in the clinical trial for BCR/ABL (Breakpoint Cluster Region/Abelson)-positive leukemia or HER2/NEU+ (Human Epidermal growth factor Receptor 2) breast cancer [56]. The gene discussed is ERBB2; the disease is leukemia.