PTEN and neoplasm: The action of PI3K is negatively regulated by PTEN (phosphatase and tensin homologue deleted on chromosome 10), a tumor suppressor gene encoding a phosphatase, which dephosphorylates phosphatidylinositol (3,4,5)-trisphosphate (PtdIns (3,4,5)P3 or PIP3) to PIP2 (PtdIns(4,5)P2) [13].