title: Insulin use and cancer risk in patients with type 2 diabetes: a systematic review and meta-analysis of observational studies.
abstract: OBJECTIVE
  To determine whether data from observational studies supports the hypothesis of an increased risk of overall and site-specific cancer among individuals with diabetes using exogenous insulin therapies.
  
  
  METHODS
  We conducted a comprehensive search of nine key biomedical databases for all years up to December 2011, restricted to the English language. Data from cohort and nested case-control studies were included in random effects meta-analyses of site-specific and overall cancer incidence comparing ever use and new use of: (1) insulin to no insulin and; (2) insulin glargine to other insulins.
  
  
  RESULTS
  The search yielded 3052 unique citations, of which 19 were selected for inclusion, representing data for 1,332,120 people and 41,947 cancers. Pancreatic cancer risk was increased among new users of insulin (RR: 3.18, 95%CI: 3.27-3.71, I(2)=32%). New use of insulin glargine was associated with an increased risk of pancreatic cancer (RR: 1.63, 95%CI: 1.05-2.51, I(2)=0%) and prostate cancers (RR: 2.68, 95%CI: 1.50-4.79, I(2)=0%) but a decreased risk of colorectal cancer (RR: 0.78, 95%CI: 0.64-0.94, I(2)=15%).
  
  
  CONCLUSIONS
  New use of insulin or insulin glargine was associated with an increased risk of pancreatic cancer, possibly due to reverse causality. New use of insulin glargine was associated with a decreased risk of colorectal cancer but an increased risk of prostate cancer. Our results should be interpreted with caution due to limitations of included studies.
authors.affiliation: Department of Public Health Sciences, University of Alberta, 2-040 Li Ka Shing Center Edmonton, Alberta, T6G 2E1 Canada.
authors.forename: I N
authors.initials: IN
authors.lastname: Colmers
authors.forename: S L
authors.initials: SL
authors.lastname: Bowker
authors.forename: L A
authors.initials: LA
authors.lastname: Tjosvold
authors.forename: J A
authors.initials: JA
authors.lastname: Johnson
mesh_terms: D016022:Case-Control Studies; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy* / Q000453:epidemiology*; D006801:Humans; D007328:Insulin / Q000008:administration & dosage*; D009369:Neoplasms / Q000453:epidemiology*; D012307:Risk Factors
chemical_list: D007328:Insulin