Potential mechanisms of metformin anticancer effects include: (1) modifications of systemic metabolism, including a reduction of blood glucose and insulin, which sustain cancer cell growth by fueling cell metabolism; (2) direct, cell-autonomous anticancer effects, which are mediated by the inhibition of mitochondrial metabolism and ATP production, with the consequent impairment of intracellular energetic status and inhibition of mTOR, protein and fatty acid biosynthesis. This evidence concerns the gene MTOR and cancer.