ABSTRACT
Metformin is a first-line drug for the treatment of type 2 diabetes mellitus. Recently, some clinical studies have been published reporting a reduced incidence of various neoplastic disease (eg. breast cancer, endometrial cancer and gastrointestinal cancer) in diabetic or nondiabetic patients treated with metformin. Metformin inhibits the mammalian target of rapamycin by activating liver kinase B1 (LKB1)/adenosine 5'-monophosphate-activated protein kinase (AMPK) or decreases blood insulin levels, resulting in inhibition of cancer cell growth. There are also many other mechanisms involved in anti-tumor effect of metformin. Although metformin has significant effect on cancers, the prospects for it as an alternative treatment modality and mechanism in various kinds of tumors need further research.