PTEN loss of function is associated with inherited cancer predisposition syndromes (for example, Cowden’s disease) and also occurs in a wide variety of sporadic human cancers [gliomas, melanomas, prostate, lung, renal, endometrial, breast and ovarian cancers, as well as T-cell acute lymphoblastic leukemia (T-ALL)] displaying Akt/mTOR up-regulation. Here, PTEN is linked to T-cell acute lymphoblastic leukemia.