STK11 and lung cancer: Although the exact mechanism was not fully understood as yet, some in vitro and in vivo studies have demonstrated with the increasing attention attached to the metformin-mediated therapy in lung cancer, that metformin may exert the antitumor activity through indirect (insulin-mediated) effects and direct effects on the inhibition of cancer cell proliferation, colony formation, migration, and invasion, and the induction of cell cycle arrest and apoptosis mediated by the ATM/LKB1/AMPK axis and mammalian target of rapamycin (mTOR)-signaling pathway [12–16].