Metformin as a cheap,safe and effective diabetes drug,has been used for many years. Recently,many studies have shown its variety inhibition of tumor cells. Its antitumor mechanism is not entirely clear;may be related to glucose metabolism and protein kinase or inflammatory cytokines mediating tumor kill-ing. Metformin has different cytotoxic effects to various tumor cell,as well as playing some auxiliary roles on other antitumor methods.