The study evaluated studies MEDLINE and AMBASE from January 1966-April 2012. Researchers reviewed 12 randomized controlled trials (n=21,595) and 41 observational studies (n=1,029,389) that met the inclusion criteria. The primary outcomes of the study were malignancies, specific site cancers, and cancer mortality associate with exposure to metformin.
According to observational studies, metformin was significantly associated with the risk of cancer death [6 studies, 24,410 patients, OR:0.65, 95%CI: 0.53-0.80], all malignancies [18 studies, 561,836 patients, OR:0.73, 95%CI: 0.61-0.88]. Exposure to metformin also significantly reduced risk in liver, pancreas, and esophagus cancer. Metformin was not associated with the risk of breast cancer, lung cancer, ovarian cancer, uterus cancer, prostate cancer, bladder cancer, kidney cancer, and melanoma. Furthermore, systematic review of randomized trials showed no significant difference of risk in patients who were taking metformin.
In conclusion, finding from the studies suggested reduction in cancer risk (35%) and cancer related mortality (31%) associated with metformin. However, these studies were not designed specifically to evaluate the potential protective action from metformin as an anticancer agent. More specific studies are required to evaluate the association between cancer and beneficial effect of metformin.
Franciosi M,Lucisano G, Lapice E, et al. Metformin Therapy and Risk of Cancer in Patients with Type 2 Diabetes: Systematic Review. PLoS One. 2013; 8(8): e71583