PTEN and esophageal cancer: Fractionated irradiation using sublethal doses administered over a period of 2 months and clonal selection for radioresistant esophageal cancer cells leads to downregulation of the phosphatase and tensin homolog (PTEN) and upregulation of phosphoinositide 3-kinase (PI3K) which is linked with inactivation of GSK-3β and is associated with elevated Snail protein, which enhances EMT (He et al., 2015a).