PTEN and thymoma: The expression of PTEN, a phosphatase that negatively regulates intracellular levels of phosphatidylinositol-3,4,5-trisphosphate and functions as a tumor suppressor by negatively regulating AKT/mTOR signaling pathways [65], was heterogenous, with no significant differences between type A and B3 thymomas and thymic carcinomas.