title: Cancer risk in diabetic patients treated with metformin: a systematic review and meta-analysis.
abstract: 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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Diabetes and Metabolic Medicine, Center Hospital, National Center for Global Health and Medicine, Tokyo, Japan. noto-tky@umin.net
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Noto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Goto
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Tsujimoto
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Noda
mesh_terms: D006801:Humans; D002986:Clinical Trials as Topic; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy; D007004:Hypoglycemic Agents / Q000627:therapeutic use; D015994:Incidence; D008687:Metformin / Q000627:therapeutic use; D009369:Neoplasms / Q000453:epidemiology; D012307:Risk Factors
chemical_list: D007004:Hypoglycemic Agents; D008687:Metformin