PTEN and cancer: The mTOR activation mechanism in human cancers is the epigenetic and genetic alteration of the upstream signaling molecules, methylation of PTEN, mutations of Ras, PIK3CA, and PTEN, and the genetic copy gain of receptor tyrosine kinase genes and other genes in the MAP kinase and PI3K/Akt pathways [30,79,80,81,82,83].