Metformin,an inexpensive and well-tolerated oral agent commonly used in the first-line treatment of type 2 diabetes,has become the focus of intense research as a candidate anticancer agent.Here,we discuss the potential of metformin in cancer therapeutics,particularly its functions in multiple signaling pathways,including AMP-activated protein kinase,mammalian target of rapamycin,insulin-like growth factor,c-Jun N-terminal kinase/mitogen-activated protein kinase(p38 MARK),human epidermal growth factor receptor-2,and nuclear factor kappaB pathways.In addition,cutting-edge targeting of cancer stem cells by metformin is summarized. Metformin, an inexpensive and well-tolerated oral agent commonly used in the first-line treatment of type 2 diabetes, has become the focus of intense research as a candidate anticancer agent. Here, we discuss the potential of metformin in cancer therapeutics, particularly its functions in multiple signaling pathways, including AMP-activated protein kinase, mammalian target of rapamycin, insulin-like growth factor, c-Jun N-terminal kinase / mitogen- activated protein kinase (p38 MARK) and nuclear factor kappaB pathways. addition, cutting-edge targeting of cancer stem cells by metformin is summarized.