AKT1 mutations have been reported in a variety of tumor types such as endometrial, lung, breast, colorectal, ovarian, and prostate cancers. The mutations are mutually exclusive from PIK3CA mutations. Increased expression and activation of AKT1 observed in many cancers is caused by a variety of different mechanisms including genomic alterations of AKT1, PIK3CA, PTEN, RAS family members, or growth factor receptors. Gain-of-function alterations of AKT1 can lead to neoplastic transformation in model systems, and is a potential target for therapeutic strategies. The E17K variant is by far the most frequent AKT1 mutation reported, implicating it as an important tumor promoting event.