PTEN is a lipid and protein phosphatase that negatively regulates the PI3K/AKT/mTOR pathway. PTEN has been reported to show nonsense and frameshift mutations in approximately 10% of adult T cell ALL patients. PTEN mutations may occur together with large deletions of PTEN which are not detected by this assay. PTEN abnormalities are thought to be more frequent in NOTCH1/FBXW7 unmutated T-ALL and appear to be mutually exclusive of NRAS/KRAS mutations in T-ALL. PTEN alterations are associated with reduced or absent protein expression and may be associated with a poor prognosis in adult T cell ALL, but not pediatric T-ALL, according to some studies. PTEN alterations appear to be infrequent among myeloid malignancies.