mTOR is activated in tumor cells by various mechanisms including growth factor surface receptor tyrosine kinases, oncogenes, and loss of tumor suppressor genes. These activating factors are known to be important for malignant transformation and progression. mTOR is particularly important in the biology of renal cancer (RCC) owing to its function in regulating HIF-1a levels. Mutation or loss of the "von Hippel Lindau" tumor-suppressor gene is common in RCC and is manifested by reduced degradation of HIF-1a. In RCC tumors, activated mTOR further exacerbates accumulation of HIF-1a by increasing synthesis of this transcription factor and its angiogenic target gene products.