MTOR and hepatocellular carcinoma: The radiotherapy resistance of HCC is mainly due to the occurrence of epithelial-mesenchymal transition (EMT) and cross-activation of Ras/Raf and phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR pathways in HCC [27, 28]; excessive activation of the pathway can enhance HCC cell survival and inhibit cell death.