Metformin, a biguanide used as first-line treatment for type 2 diabetes mellitus, lowers blood glucose by activating AMP-activated protein kinase (AMPK). AMPK activation, through the reduction of mammalian target of rapamycin (mTOR) signaling, has also been shown to inhibit cancer cell growth and proliferation (1). Thus, it is conceivable that AMPK activators such as metformin may influence human cancer risk.