title: Metformin and the risk of prostate cancer across racial/ethnic groups: a population-based cohort study.
abstract: Men with diabetes may have a lower risk of prostate cancer than men without diabetes which may be altered by metformin use or race/ethnicity.
  
  
  
  Using administrative databases, from 1994 to 2012, adult (age⩾50 years) men with diabetes were identified. Metformin exposure was defined as a time-dependent variable, stratified first into any use, and into tertiles of cumulative dose. Surname algorithms identified individuals as Chinese or non-Chinese. Multivariable Cox regression estimated the risk of prostate cancer.
  
  
  
  The cohort of 80 001 had a mean age of 64 years and median follow-up of 9 years. Chinese users of metformin aged 50-59, 60-69 and ⩾70 had similar risks of prostate cancer as non-users. Non-Chinese users aged 50-59 (adjusted hazards ratio (aHR): 0.86, 0.74 to 1.00) had a decreased risk whereas men aged 60-69 and ⩾70 did not. However, when metformin exposure was stratified into tertiles, there was no association in any strata except non-Chinese men aged 50-59 in the first (aHR: 0.68, 95% confidence interval (CI): 0.55, 0.84), second (aHR: 0.75, 95% CI: 0.61, 0.92) and third (aHR: 0.79, 95% CI: 0.64, 0.96) tertiles of metformin exposure and non-Chinese men aged 60-69 in the first (aHR: 0.81, 95% CI: 0.68, 0.95) tertiles of metformin exposure.
  
  
  
  There was no clear association between metformin and risk of prostate cancer in men with diabetes in either race/ethnicity. Our findings suggest a consistent relationship between metformin and prostate cancer across race/ethnicity.
authors.affiliation: School of Public Health, University of Alberta, Edmonton, AB, Canada.
authors.forename: C B
authors.initials: CB
authors.lastname: Chen
authors.affiliation: School of Public Health, University of Alberta, Edmonton, AB, Canada.
authors.forename: D T
authors.initials: DT
authors.lastname: Eurich
authors.affiliation: Department of Medicine, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB, Canada.
authors.forename: S R
authors.initials: SR
authors.lastname: Majumdar
authors.affiliation: School of Public Health, University of Alberta, Edmonton, AB, Canada.
authors.forename: J A
authors.initials: JA
authors.lastname: Johnson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001955:British Columbia / Q000453:epidemiology; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000150:complications* / Q000188:drug therapy; D005500:Follow-Up Studies; D006801:Humans; D007004:Hypoglycemic Agents / Q000009:adverse effects* / Q000627:therapeutic use; D008297:Male; D008687:Metformin / Q000009:adverse effects* / Q000627:therapeutic use; D008875:Middle Aged; D044382:Population Groups / Q000706:statistics & numerical data*; D011159:Population Surveillance; D016016:Proportional Hazards Models; D011471:Prostatic Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D012189:Retrospective Studies; D012306:Risk; D012959:Socioeconomic Factors
chemical_list: D007004:Hypoglycemic Agents; D008687:Metformin