Temsirolimus, an ester of sirolimus (rapamycin), selectively inhibits the kinase mammalian target of rapamycin and consequently blocks the translation of cell cycle regulatory proteins and prevents overexpression of angiogenic growth factors. Patients with advanced renal cell carcinoma (RCC) and a poor prognosis who received a once-weekly intravenous (IV) infusion of temsirolimus 25 mg, experienced significant survival benefits when compared with patients receiving standard interferon-alpha (IFNalpha) therapy in a large phase III clinical study. In this study, median overall survival was 10.9 vs. 7.3 months and objective response rates were 8.6% in temsirolimus recipients vs. 4.8% IFNalpha recipient group.Temsirolimus monotherapy recipients experienced significantly fewer grade 3 or 4 adverse events and had fewer withdrawals for adverse events than patients receiving IFNalpha.