PTEN and neoplasm: Some tumor-associated missense mutations may lead to complete loss or severe impairment of the phosphatase activity of the encoded enzyme.75–77 Many tumor-derived PTEN mutants retain partial or complete catalytic function, suggesting that alternative mechanisms can lead to the inactivation of PTEN.78 In addition to its own genetic alterations, PTEN gene expression is also regulated at epigenetic,79 transcriptional,80–82 post-transcriptional83–86, and post-translational87–92 levels as well as by protein–protein interactions.93,94