MTOR and cancer: Several studies have revealed that cellular stress (such as hypoxia), cytokines (such as TGF-β), or activation of the mTOR pathway are able to increase the expression of CSC surface markers and phenotypes in certain bulk tumor cells [36], [48], [57], [58], indicating that cell-extrinsic environmental factors may reprogram conventional tumor cells to cells with stem cell-like properties in the course of cancer development.