title: Performance of systematic and non-systematic ('opportunistic') screening mammography: a comparative study from Denmark.
abstract: OBJECTIVE
  Evaluation and comparison of the performance of organized and opportunistic screening mammography.
  
  
  METHODS
  Women attending screening mammography in Denmark in 2000. The study included 37,072 women attending organized screening. Among these, 320 women were diagnosed with breast cancer during follow-up. Opportunistic screening was attended by 2855 women with 26 women being diagnosed with breast cancer. Data on women attending screening were linked with information on cancer status. Each woman was followed with respect to diagnosis of breast cancer (invasive as well as in situ) for a period of two years. Screening outcome and cancer status during follow-up were combined to assess whether the result of the examination was true-positive, true-negative, false-positive or false-negative. Based on this classification, age-adjusted sensitivity and specificity of organized and opportunistic screening were calculated.
  
  
  RESULTS
  Defining BI-RADS(trade mark) 4-5 as a positive screening outcome, the overall sensitivity of opportunistic screening was 33.6% and the specificity was 99.1%. Using BI-RADS(trade mark) 3-5 as positive, the sensitivity was 37.4% and the specificity was 97.9%. Organized screening (which was not categorized according to BI-RADS(trade mark)) had an overall sensitivity of 67.2% and a specificity of 98.4%.
  
  
  CONCLUSIONS
  Our study showed a considerably higher sensitivity in organized screening than in opportunistic screening, while the specificity was fairly similar in the two settings. The findings support implementation of population-based breast screening programmes, as recommended in the 'European guidelines for quality assurance in breast cancer screening and diagnosis'.
authors.affiliation: Institute of Public Health, University of Copenhagen, Øster Farimagsgade 5, opg B, Copenhagen K, Denmark. k.bihrmann@pubhealth.ku.dk
authors.forename: Kristine
authors.initials: K
authors.lastname: Bihrmann
authors.forename: Allan
authors.initials: A
authors.lastname: Jensen
authors.forename: Anne Helene
authors.initials: AH
authors.lastname: Olsen
authors.forename: Sisse
authors.initials: S
authors.lastname: Njor
authors.forename: Walter
authors.initials: W
authors.lastname: Schwartz
authors.forename: Ilse
authors.initials: I
authors.lastname: Vejborg
authors.forename: Elsebeth
authors.initials: E
authors.lastname: Lynge
mesh_terms: D001943:Breast Neoplasms / Q000175:diagnosis*; D003718:Denmark; D005260:Female; D006801:Humans; D008327:Mammography; D008403:Mass Screening / Q000379:methods*; D012680:Sensitivity and Specificity