PTEN (phosphatase and tensin homologue deleted on chromosome ten) phosphatase is a tumor suppressor gene implicated in a wide variety of human cancers. PTEN encodes the 403 amino acid polypeptide originally described as a dual-specificity protein phosphatase. The main substrates of PTEN are inositol phospholipids generated by the activation of the phosphoinositide 3 kinase (PI3K). PTEN is a major negative regulator of the PI3K/Akt signaling pathway.