FBXW7 is a tumor suppressor gene responsible for the degradation of several proto-oncogenes and is inactivated by mutation in various cancers, most frequently in endometrial and colorectal cancers. Substrates of FBXW7 include the proteins c-MYC, mTOR, NOTCH1, cyclin-E, and JUN, which are instrumental in the regulation of cell division, differentiation and growth, and which are often inappropriately activated in cancer. Inactivation of FBXW7 by mutation or copy number loss results in aberrant accumulation of the above oncoproteins, which subsequently contributes to malignant transformation. mTOR is one of the substrates of FBXW7-mediated protein degradation, and loss of function of FBXW7 increases the levels of total and activated mTOR. Most mutations in FBXW7 are point mutations that disrupt substrate binding, while <10% are small deletions or insertions. FBXW7 is altered in 17% of colorectal adenocarcinomas. The FBXW7 R465H variant is considered to be likely oncogenic. Preclinical data have suggested that inactivating mutations of FBXW7 could predict sensitivity to the mTOR inhibitor rapamycin. A single study has reported only limited activity in phase I trials using mTOR inhibitors in patients with advanced cancers including colorectal cancer. The clinical utility remains unknown.