MTOR and cancer: All these pathways are believed to contribute to reducing cancer cell growth and progression.19–21 In addition, metformin directly suppresses mitochondrial activity and reduces the availability of adenosine triphosphate (ATP) and, more in general, those biosynthetic precursors required for cell growth.22–24 Valuable studies indicated that metformin acted as an inhibitor of the mammalian target of rapamycin (mTOR) signaling25–28 and modulates the PD-L1/PD-1 axis via AMPK-dependent and independent mechanisms.18,29,30