title: Missed and true interval and screen-detected breast cancers in a population based screening program.
abstract: OBJECTIVE
  To increase radiologic knowledge, the distribution of mammographic features on prior screening mammograms of missed interval and screen-detected cancers was compared to the distribution on diagnostic mammograms of screen-detected cancers. The same variables were compared on mammograms of discordant and concordant screen-detected cancers.
  
  
  METHODS
  The study was performed in Møre og Romsdal County, Norway, as a part of the quality assurance of the Norwegian Breast Cancer Screening Program. Women were screened using analog techniques and diagnosed from 2002 to 2008. Prior and diagnostic mammograms of 81 interval and 123 screen-detected breast cancers in women aged 50 to 71 years were retrospectively reviewed and classified as either missed or true by four experienced breast radiologists. Mammographic features were classified according to a modified Breast Imaging Reporting and Data System.
  
  
  RESULTS
  Thirty percent (24 of 81) of the interval cancers and 21% (26 of 123) of the screen-detected cancers were classified as missed. Calcifications, alone or in association with mass or asymmetry, tended to be more common on prior mammograms of missed cancers compared to diagnostic mammograms of screen-detected cancers (34% [17 of 50] vs 21% [26 of 123], P = .114), whereas an opposite trend was seen for mass (54% [27 of 50] vs 68% [84 of 123], P = .109). Similar results were seen when comparing discordant and concordant cancers.
  
  
  CONCLUSIONS
  Calcifications represent a challenge in the interpretation of screening mammograms. For educational purposes, the importance of reviewing both interval and screen-detected cancers is obvious. Knowledge gained from systematic reviews might reduce the number of missed cancers on mammographic screening. Performing reviews according to established guidelines would make it possible to compare results across screening programs.
authors.affiliation: Department of Radiology, Aalesund Hospital, Helse Sunnmøre HF, Aalesund, Norway. sorohoff@gmail.com
authors.forename: Solveig Roth
authors.initials: SR
authors.lastname: Hoff
authors.forename: Jon Helge
authors.initials: JH
authors.lastname: Samset
authors.forename: Anne-Line
authors.initials: AL
authors.lastname: Abrahamsen
authors.forename: Einar
authors.initials: E
authors.lastname: Vigeland
authors.forename: Olbjørn
authors.initials: O
authors.lastname: Klepp
authors.forename: Solveig
authors.initials: S
authors.lastname: Hofvind
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008327:Mammography / Q000706:statistics & numerical data*; D008403:Mass Screening / Q000706:statistics & numerical data*; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D015588:Observer Variation; D015995:Prevalence; D015203:Reproducibility of Results; D018570:Risk Assessment; D012307:Risk Factors; D012680:Sensitivity and Specificity