Metformin: A candidate for the treatment of gynecological tumors based on drug repositioning.

Metformin is a first-line drug used for the treatment of type 2 diabetes. Recently, metformin has been reported to reduce the carcinogenic risk and inhibit tumor cell growth in glioma and breast cancer. The anticancer action of metformin involves the enhancement of phosphorylation of liver kinase B1, activation of adenosine monophosphate-activated protein kinase and inhibition of mammalian target of rapamycin, which reduces cell growth. Metformin is anticipated to exert antitumor effects in gynecological cancer, and its efficacy for the treatment of endometrial, breast and ovarian cancer has been suggested in preclinical studies and clinical trials. Although the effect of metformin on cervical cancer remains to be examined in clinical trials, its antitumor effects have been reported in preclinical studies. Thus, the use of metformin for the treatment of gynecological cancer may become a successful example of drug repositioning, following establishment of the drug's antitumor effects, risk evaluation, screening and validation of efficacy.