title: Metformin does not affect cancer risk: a cohort study in the U.K. Clinical Practice Research Datalink analyzed like an intention-to-treat trial.
abstract: OBJECTIVE
  Meta-analyses of epidemiologic studies have suggested that metformin may reduce cancer incidence, but randomized controlled trials did not support this hypothesis.
  
  
  METHODS
  A retrospective cohort study, Clinical Practice Research Datalink, was designed to investigate the association between use of metformin compared with other antidiabetes medications and cancer risk by emulating an intention-to-treat analysis as in a trial. A total of 95,820 participants with type 2 diabetes who started taking metformin and other oral antidiabetes medications within 12 months of their diagnosis (initiators) were followed up for first incident cancer diagnosis without regard to any subsequent changes in pharmacotherapy. Cox proportional hazards models were used to estimate multivariable-adjusted hazard ratios (HR) and 95% CI.
  
  
  RESULTS
  A total of 51,484 individuals (54%) were metformin initiators and 18,264 (19%) were sulfonylurea initiators, and 3,805 first incident cancers were diagnosed during a median follow-up time of 5.1 years. Compared with initiators of sulfonylurea, initiators of metformin had a similar incidence of total cancer (HR 0.96; 95% CI 0.89-1.04) and colorectal (HR 0.92; 95% CI 0.76-1.13), prostate (HR 1.02; 95% CI 0.83-1.25), lung (HR 0.85; 95% CI 0.68-1.07), or postmenopausal breast (HR 1.03; 95% CI 0.82-1.31) cancer or any other cancer.
  
  
  CONCLUSIONS
  In this large study, individuals with diabetes who used metformin had a similar risk of developing cancer compared with those who used sulfonylureas.
authors.affiliation: Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece Cancer Epidemiology Unit, University of Oxford, Oxford, U.K. ktsilidi@cc.uoi.gr ktsilidis@gmail.com.
authors.forename: Konstantinos K
authors.initials: KK
authors.lastname: Tsilidis
authors.affiliation: Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece.
authors.forename: Despoina
authors.initials: D
authors.lastname: Capothanassi
authors.affiliation: Clinical Trial Service Unit, University of Oxford, Oxford, U.K.
authors.forename: Naomi E
authors.initials: NE
authors.lastname: Allen
authors.affiliation: Lipid Disorders Clinic, Department of Internal Medicine, University Hospital of Ioannina, Ioannina, Greece.
authors.forename: Evangelos C
authors.initials: EC
authors.lastname: Rizos
authors.affiliation: Division of Epidemiology, University of Texas School of Public Health, Houston, TX.
authors.forename: David S
authors.initials: DS
authors.lastname: Lopez
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, St Mary's Campus, London, U.K. University College London Institute of Child Health, Centre for Paediatric Epidemiology and Biostatistics, London, U.K.
authors.forename: Karin
authors.initials: K
authors.lastname: van Veldhoven
authors.affiliation: Human Genetics Foundation (HuGeF), Turin, Italy.
authors.forename: Carlotta
authors.initials: C
authors.lastname: Sacerdote
authors.affiliation: Imperial Clinical Trials Unit, School of Public Health, Imperial College London, St Mary's Hospital, London, U.K.
authors.forename: Deborah
authors.initials: D
authors.lastname: Ashby
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, St Mary's Campus, London, U.K. Human Genetics Foundation (HuGeF), Turin, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Vineis
authors.affiliation: Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, St Mary's Campus, London, U.K.
authors.forename: Ioanna
authors.initials: I
authors.lastname: Tzoulaki
authors.affiliation: Stanford Prevention Research Center, Department of Medicine; Department of Health Research and Policy, Stanford University School of Medicine; and Department of Statistics, Stanford University School of Humanities and Sciences, Stanford, CA.
authors.forename: John P A
authors.initials: JP
authors.lastname: Ioannidis
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016208:Databases, Factual; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy*; D005260:Female; D005500:Follow-Up Studies; D006295:Health Resources; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use*; D015994:Incidence; D057194:Intention to Treat Analysis; D008297:Male; D008687:Metformin / Q000627:therapeutic use*; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology*; D011379:Prognosis; D012189:Retrospective Studies; D012307:Risk Factors; D013453:Sulfonylurea Compounds / Q000627:therapeutic use*; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D007004:Hypoglycemic Agents; D013453:Sulfonylurea Compounds; D008687:Metformin