title: Seventeen-years overview of breast cancer inside and outside screening in Denmark.
abstract: BACKGROUND
  Long-term data on breast cancer detection in mammography screening programs are warranted to better understand the mechanisms by which screening changes the breast cancer pattern in the population. We aimed to analyze 17 years of breast cancer detection rates inside and outside screening in two Danish regions, emphasizing the influence of organizational differences of screening programs on the outcomes.
  
  
  METHODS
  We used data from two long-standing population-based mammography screening programs, Copenhagen and Fyn, in Denmark. Both programs offered biennial screening to women aged 50-69 years. We identified targeted, eligible, invited and participating women. We calculated screening detection and interval cancer rates for participants, and breast cancer incidence in non-screened women (= targeted women excluding participants) by biennial invitation rounds. Tumor characteristics were tabulated for each of the three groups of cancers.
  
  
  RESULTS
  Start of screening resulted in a prevalence peak in participants, followed by a decrease to a fairly stable detection rate in subsequent invitation rounds. A similar pattern was found for breast cancer incidence in non-screened women. In Fyn, non-screened women even had a higher rate than screening participants during the first three invitation rounds. The interval cancer rate was lower in Copenhagen than in Fyn, with an increase over time in Copenhagen, but not in Fyn. Screen-detected cancers showed tumor features related with a better prognosis than tumors detected otherwise, as more than 80% were smaller than 20 mm and estrogen receptor positive.
  
  
  CONCLUSIONS
  Data from two long-standing population-based screening programs in Denmark illustrated that even if background breast cancer incidence and organization were rather similar, performance indicators of screening could be strongly influenced by inclusion criteria and participation rates. Detection rates should be interpreted with caution as they may be biased by selection into the screening population.
authors.affiliation: Department of Public Health, University of Copenhagen, Denmark. LDomingo@parcdesalutmar.cat
authors.forename: Laia
authors.initials: L
authors.lastname: Domingo
authors.forename: Katja Kemp
authors.initials: KK
authors.lastname: Jacobsen
authors.forename: My
authors.initials: M
authors.lastname: von Euler-Chelpin
authors.forename: Ilse
authors.initials: I
authors.lastname: Vejborg
authors.forename: Walter
authors.initials: W
authors.lastname: Schwartz
authors.forename: Maria
authors.initials: M
authors.lastname: Sala
authors.forename: Elsebeth
authors.initials: E
authors.lastname: Lynge
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology* / Q000378:metabolism; D003718:Denmark / Q000453:epidemiology; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008327:Mammography; D008403:Mass Screening / Q000458:organization & administration*; D008875:Middle Aged; D011379:Prognosis; D015397:Program Evaluation; D011960:Receptors, Estrogen / Q000378:metabolism
chemical_list: D011960:Receptors, Estrogen