PTEN and neoplasm: PTEN is one of the most frequently silenced tumor suppressors2, 3 and is haploinsufficient,4, 5 with subtle changes in PTEN expression altering cancer susceptibility.6 PTEN is disrupted in many sporadic tumors as well as in cancer predisposition syndromes,7, 8 and PTEN knockout mice show increased susceptibility to multiple malignancies.9, 10, 11 PTEN exhibits both lipid and protein phosphatase activity and has manifold tumor suppressor functions (reviewed in Song and Salmena3), including a major role in dephosphorylation of PtdIns(3,4,5)P3.