PTEN and cancer: As exon 5 encodes a phosphatase domain, a mutation in exon 5 abrogates the tumor suppressor role of PTEN. 55,56 Moreover, sporadic PTEN mutations are observed in different cancer types such as glioblastoma multiforme (GBM) (19%–32%), endometrial (21%), prostate (17%–21%), malignant melanoma (14%–16%), and breast (4%–11%).57