title: Antidiabetic medications and the risk of colorectal cancer in patients with diabetes mellitus: a systematic review and meta-analysis.
abstract: BACKGROUND
  Antidiabetic medications (ADM) may modify colorectal cancer risk in patients with diabetes mellitus. We performed a systematic review and meta-analysis, evaluating the effect of metformin, thiazolidinediones (TZD), sulfonylureas, and insulin on colorectal cancer risk in diabetic patients.
  
  
  METHODS
  We conducted a systematic search of multiple bibliographic databases, up to September 2012, for articles that evaluated exposure to metformin, TZD, sulfonylureas, and insulin, reported colorectal cancer risk in patients with diabetes mellitus, and reported OR or provided data for their estimation. Summary OR estimates with 95% confidence intervals (CI) were estimated using the random-effects model.
  
  
  RESULTS
  Fifteen studies reporting 13,871 cases of colorectal cancer in 840,787 patients with diabetes mellitus were included. Meta-analysis of observational studies showed an 11% reduction in colorectal cancer risk associated with metformin use (n = 9 studies; OR, 0.89; 95% CI, 0.81-0.99), whereas TZD use was not associated with colorectal cancer risk (n = 5 studies; OR, 0.96; 95% CI, 0.87-1.05). Conversely, a trend toward higher colorectal cancer risk was observed with sulfonylurea (n = 7 studies; OR, 1.11; 95% CI, 0.97-1.26) and insulin (n = 9 studies; OR, 1.33; 95% CI, 0.91-1.94) use, although these associations were not statistically significant. There was considerable heterogeneity across studies, partly explained by study location and adjustment for concomitant use of other ADMs. Post-hoc analysis of randomized controlled trials did not reveal any significant association between ADM and colorectal cancer risk.
  
  
  CONCLUSIONS
  Meta-analysis of published studies supports a protective association between metformin use and colorectal cancer risk in patients with diabetes mellitus.
  
  
  CONCLUSIONS
  Clinical trials on the chemopreventive effect of metformin against colorectal cancer are warranted.
authors.affiliation: Authors' Affiliations: Division of Gastroenterology and Hepatology, Department of Medical Oncology, Division of Preventive Medicine, Mayo Clinic, Rochester, Minnesota; and Department of Internal Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania.
authors.forename: Siddharth
authors.initials: S
authors.lastname: Singh
authors.forename: Harkirat
authors.initials: H
authors.lastname: Singh
authors.forename: Preet Paul
authors.initials: PP
authors.lastname: Singh
authors.forename: M Hassan
authors.initials: MH
authors.lastname: Murad
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Limburg
mesh_terms: D015179:Colorectal Neoplasms / Q000453:epidemiology*; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy / Q000453:epidemiology*; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage* / Q000009:adverse effects
chemical_list: D007004:Hypoglycemic Agents