Previous studies demonstrated that metformin may inhibit mammalian target of rapamycin (mTOR) through activating the liver kinase B1 (LKB1)/AMPK pathway; it may suppress the synthesis of proteins, downregulate the level of circulating insulin, restrain the reply of unfolded proteins, eliminate cancer stem cells, activate the immune system, or cause cell cycle arrest and/or apoptosis [49,50]. Here, STK11 is linked to cancer.