Preventive and (Neo)Adjuvant Therapeutic Effects of Metformin on Cancer

Metformin, the first-line antidiabetic drug, has become an attractive candidate in cancer therapy since retrospective clinical investigations reported that patients with type 2 diabetes receiving metformin had lower incidence of cancer than those with other glucose lowering drugs. In line with this, preclinical studies have demonstrated that the antitumor activity of metformin could proceed through several mechanisms. Thus far, metformin has been used in cancer prevention with reduced risk as consequence and treatment of various cancers as an adjuvant or neoadjuvant drug. Thus, existing data support the beneficial effects of metformin on many types of cancers such as reducing metastasis and mortality and improving pathological responses and survival rates. However, some reports do not support this and even show adverse effects. The discrepancy may be attributed to expression levels of its transporters or genetic background. Hence, this chapter briefly reviews information on the mechanism of metformin action and summarizes both completed and ongoing clinical trials in an attempt to evaluate the value of metformin in prevention and treatment of various cancer types.