PTEN (phosphatase and tensin homolog) is a tumor suppressor with roles in the cell cycle, growth, DNA repair, cell survival and regulation of the AKT-mTOR pathway. Simple variants in PTEN are seen in about 6% of all tumors, including 39% of endometrial tumors, 13% of central nervous system tumors, 8.5% of skin tumors, and 7% of prostate and breast tumors. PI3K inhibitors have shown antitumor activity in preclinical studies of PTEN-deficient breast and prostate cancer, but not in a study of endometrial cancer.