title: Effect of organised mammography screening on stage-specific incidence in Norway: population study.
abstract: BACKGROUND
  We aimed to estimate the effect of organised mammography screening on breast cancer stage distribution by comparing changes in women eligible for screening, based on birth cohort, to the concurrent changes in younger, ineligible women.
  
  
  METHODS
  In an open cohort study in Norway, which introduced national mammography screening county-by-county from 1995 to 2004, we identified women (n=49 883) diagnosed with in situ or invasive breast cancer (ICD10 codes: D05 or C50) during the period 1987-2011 and born between 1917 and 1980. We estimated relative incidence rate ratios (rIRRs) comparing the development in the screening vs historic group to the younger vs younger historic group.
  
  
  RESULTS
  Including the compensatory drop, eligible women experienced a 68% higher increase in localised cancers (rIRR=1.68, 95% confidence interval (CI): 1.51-1.87) than younger women, while the increase in incidence of advanced cancers was similar (rIRR=1.11, 95% CI: 0.90-1.36). Excluding the prevalence round, eligible women experienced a 60% higher increase in localised cancers (rIRR=1.60, 95% CI: 1.42-1.79), while the increase in incidence of advanced cancers remained similar (rIRR=1.08, 95% CI: 0.86-1.35).
  
  
  CONCLUSIONS
  Introduction of organised mammography screening was followed by a significant increase in localised and no change in advanced-stage cancers in women eligible for screening relative to younger, ineligible women.
authors.affiliation: Department of Public Health, Aarhus University, Bartholins Allé 2, Aarhus C DK-8000, Denmark.
authors.forename: Mette L
authors.initials: ML
authors.lastname: Lousdal
authors.affiliation: Department of Health Management and Health Economics, Oslo University, PO Box 1089, Oslo N-0317, Norway.
authors.forename: Ivar S
authors.initials: IS
authors.lastname: Kristiansen
authors.affiliation: The Cancer Registry of Norway, PO Box 5313, Oslo N-0304, Norway.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Møller
authors.affiliation: Department of Public Health, Aarhus University, Bartholins Allé 2, Aarhus C DK-8000, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Støvring
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000473:pathology; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000473:pathology; D015331:Cohort Studies; D055088:Early Detection of Cancer / Q000379:methods*; D005260:Female; D006801:Humans; D015994:Incidence; D008327:Mammography / Q000379:methods*; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology
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