title: Increased risk of breast cancer in women with false-positive test: the role of misclassification.
abstract: BACKGROUND
  Studies have shown that women with a false-positive result from mammography screening have an excess risk for breast cancer compared with women who only have negative results. We aimed to assess the excess risk of cancer after a false-positive result excluding cases of misclassification, i.e. women who were actually false-negatives instead of false-positives.
  
  
  METHODS
  We used data from the Copenhagen Mammography Screening Programme, Denmark. The study population was the 295 women, out of 4743 recalled women from a total of 58,003 participants, with a false-positive test during the screening period 1991-2005 and who later developed breast cancer. Cancers that developed in the same location as the finding that initially caused the recall was studied in-depth in order to establish whether there had been misclassification.
  
  
  RESULTS
  Seventy-two cases were found to be misclassified. When the women with misclassified tests had been excluded, there was an excess risk of breast cancer of 27% (RR=1.27, 95% confidence interval (CI), 1.11-1.46) among the women with a false-positive test compared to women with only negative tests. Women with a false-positive test determined at assessment had an excess risk of 27%, while false-positives determined at surgery had an excess risk of 30%.
  
  
  CONCLUSIONS
  The results indicate that the increased risk is not explained only by misclassification. The excess risk remains for false-positives determined at assessment as well as at surgery, which favours some biological susceptibility. Further research into the true excess risk of false positives is warranted.
authors.affiliation: Department of Public Health, University of Copenhagen, Øster Farimagsgade 5, DK-1014 Copenhagen, Denmark. Electronic address: myeu@sund.ku.dk.
authors.forename: My
authors.initials: M
authors.lastname: von Euler-Chelpin
authors.affiliation: Department of Radiology, University Hospital of Copenhagen, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark. Electronic address: rqjps480@yahoo.co.jp.
authors.forename: Megumi
authors.initials: M
authors.lastname: Kuchiki
authors.affiliation: Department of Radiology, University Hospital of Copenhagen, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark. Electronic address: Ilse.Vejborg@regionh.dk.
authors.forename: Ilse
authors.initials: I
authors.lastname: Vejborg
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology; D003718:Denmark; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008327:Mammography; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D012306:Risk; D013997:Time Factors
keywords: Breast cancer; False-positive; Mammography; Misclassification; Screening