title: Metformin and the incidence of prostate cancer in patients with type 2 diabetes.
abstract: BACKGROUND
  Several in vitro studies have indicated that metformin may reduce the risk of prostate cancer; however, epidemiologic studies have been inconclusive. The objective of this study was to determine whether metformin decreases the risk of prostate cancer in patients with type 2 diabetes.
  
  
  METHODS
  A nested case-control analysis was conducted within a population-based cohort from the UK General Practice Research Database. The cohort included patients over the age of 40 who were prescribed a first oral hypoglycemic agent (OHA) between 1988 and 2009. Cases of prostate cancer were matched up to ten controls on year of birth, date of cohort entry, and duration of follow-up. Adjusted rate ratios (RR) were estimated using conditional logistic regression.
  
  
  RESULTS
  The cohort included 63,049 incident users of OHAs, in which 739 cases of prostate cancer were matched to 7,359 controls. Metformin use did not decrease the risk of prostate cancer (RR: 1.23, 95% CI: 0.99-1.52). In secondary analyses, prostate cancer risk was found to increase as a function of the number of metformin prescriptions received (one to seven prescriptions: RR: 1.05, 95% CI: 0.80-1.37; seven to eighteen prescriptions: RR: 1.29, 95% CI: 0.99-1.69; eighteen to thirty-six prescriptions: RR: 1.37, 95% CI: 1.04-1.81; more than thirty-six prescriptions: RR: 1.40, 95% CI: 1.03-1.89).
  
  
  CONCLUSIONS
  The results of this study indicate that metformin does not reduce the risk of prostate cancer in patients with type 2 diabetes.
  
  
  CONCLUSIONS
  The secondary analyses need to be interpreted with caution given the inverse association between type 2 diabetes and prostate cancer.
authors.affiliation: Sir Mortimer B. Davis Jewish General Hospital Centre for Clinical Epidemiology and Community Studies 3755 Côte Sainte-Catherine, H-425.1 Montreal, Quebec, Canada H3T 1E2. laurent.azoulay@mcgill.ca
authors.forename: Laurent
authors.initials: L
authors.lastname: Azoulay
authors.forename: Sophie
authors.initials: S
authors.lastname: Dell'Aniello
authors.forename: Bruno
authors.initials: B
authors.lastname: Gagnon
authors.forename: Michael
authors.initials: M
authors.lastname: Pollak
authors.forename: Samy
authors.initials: S
authors.lastname: Suissa
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D005500:Follow-Up Studies; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage*; D015994:Incidence; D008297:Male; D008687:Metformin / Q000008:administration & dosage*; D008875:Middle Aged; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000453:epidemiology*; D012307:Risk Factors; D012680:Sensitivity and Specificity; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D007004:Hypoglycemic Agents; D008687:Metformin