PTEN is an obligate haplo-insufficient tumor suppressor gene and is mutated in a large number of cancers. It encodes a phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase. It negatively regulates intracellular levels of phosphatidylinositol-3,4,5-trisphosphate in cells and functions as a tumor suppressor by negatively regulating AKT/mTOR signaling pathway. Cancer-associated alterations in this gene often result in loss of PTEN protein and upregulation of the PI3K/AKT/mTOR pathway. PTEN mutations have been reported in 15% of anaplastic thyroid cancer. Germline mutations of PTEN lead to inherited hamartoma and Cowden syndrome. Patients with Cowden syndrome have an increased risk of developing epithelial thyroid cancer, follicular carcinoma being the most common, of up to 10% compared to <1% in the general population. The PTEN I101T has been observed in a variety of cancer types. One study identified the PTEN I101T variant in 1 out of 172 patients with germ line PTEN mutations. Of note, an in vitro studied observed that the PTEN I101T variant reduced the half-life of PTEN as well as significantly reduced its activity. Clinical trials using PI3K-beta inhibitor are available for patients with PTEN-deficient tumors.

PTEN is a tumor suppressor gene, and loss of PTEN results in upregulation of the PI3K/ AKT pathway. Loss of PTEN is most commonly due to promoter hypermethylation, while homozygous deletion and nonsense mutations with loss of heterozygosity (LOH) may also occur. PTEN mutations may occur in multiple exons. Somatic mutations in PTEN have been found in 4-8% of non-small cell carcinomas (NSCLC) including adenocarcinomas and squamous cell carcinomas. In preclinical studies, PTEN loss is associated with decreased sensitivity of EGFR mutant lung tumors to EGFR TKIs. Clinical trials assessing the efficacy of PI3K inhibitors in PTEN loss are being explored. The PTENI101T has been observed in a variety of cancer types, most frequently gliomas, and has been predicted to be pathogenic. However, one study identified the PTEN I101T variant in 1 out of 172 patients with germline PTEN mutations.