Abstract: Metformin is the first-line agent in the treatment of type 2 diabetes mellitus(DM).Several clinical epidemiological studies have recently reported the reduced incidence of cancer and cancer mortality rate in type 2 DM patients treated with metformin compared with those treated with insulin or other oral antidiabetic agents.Laboratory studies have shown that metformin inhibits the growth of several types of cancer cells both in vitro and in vivo.Metformin possibly targets the insulin/IGF-1 axis and indirectly inhibits cancer cell growth.In addition, metformin directly inhibits the growth of cancer cells.These results suggest that metformin has anti -cancer effect and may be used as a new adjuvant therapy drug.