TY - JOUR T1 - Cancer Risk in Diabetic Patients Treated with Metformin: A Systematic Review and Meta-analysis A1 - Noto, Hiroshi A1 - Goto, Atsushi A1 - Tsujimoto, Tetsuro A1 - Noda, Mitsuhiko Y1 - 2012/03/20 N2 - Background A growing body of evidence has suggested that metformin potentially reduces the risk of cancer. Our objective was to enhance the precision of estimates of the effect of metformin on the risk of any-site and site-specific cancers in patients with diabetes. Methods/Principal Findings We performed a search of MEDLINE, EMBASE, ISI Web of Science, Cochrane Library, and ClinicalTrials.gov for pertinent articles published as of October 12, 2011, and included them in a systematic review and meta-analysis. We calculated pooled risk ratios (RRs) for overall cancer mortality and cancer incidence. Of the 21,195 diabetic patients reported in 6 studies (4 cohort studies, 2 RCTs), 991 (4.5%) cases of death from cancer were reported. A total of 11,117 (5.3%) cases of incident cancer at any site were reported among 210,892 patients in 10 studies (2 RCTs, 6 cohort studies, 2 case-control studies). The risks of cancer among metformin users were significantly lower than those among non-metformin users: the pooled RRs (95% confidence interval) were 0.66 (0.49–0.88) for cancer mortality, 0.67 (0.53–0.85) for all-cancer incidence, 0.68 (0.53–0.88) for colorectal cancer (n = 6), 0.20 (0.07–0.59) for hepatocellular cancer (n = 4), 0.67 (0.45–0.99) for lung cancer (n = 3). Conclusion/Significance The use of metformin in diabetic patients was associated with significantly lower risks of cancer mortality and incidence. However, this analysis is mainly based on observational studies and our findings underscore the more need for long-term RCTs to confirm this potential benefit for individuals with diabetes. JF - PLOS ONE JA - PLOS ONE VL - 7 IS - 3 UR - https://doi.org/10.1371/journal.pone.0033411 SP - e33411 EP - PB - Public Library of Science M3 - doi:10.1371/journal.pone.0033411 ER -