title: A simple way to measure the burden of interval cancers in breast cancer screening.
abstract: BACKGROUND
  The sensitivity of a mammography program is normally evaluated by comparing the interval cancer rate to the expected breast cancer incidence without screening, i.e. the proportional interval cancer rate (PICR). The expected breast cancer incidence in absence of screening is, however, difficult to estimate when a program has been running for some time. As an alternative to the PICR we propose the interval cancer ratio ICR=intervalcancersintervalcancers+screendetectedcancers. We validated this simple measure by comparing it with the traditionally used PICR.
  
  
  METHODS
  We undertook a systematic review and included studies: 1) covering a service screening program, 2) women aged 50-69 years, 3) observed data, 4) interval cancers, women screened, or interval cancer rate, screen detected cases, or screen detection rate, and 5) estimated breast cancer incidence rate of background population. This resulted in 5 papers describing 12 mammography screening programs.
  
  
  RESULTS
  Covering initial screens only, the ICR varied from 0.10 to 0.28 while the PICR varied from 0.22 to 0.51. For subsequent screens only, the ICR varied from 0.22 to 0.37 and the PICR from 0.28 to 0.51. There was a strong positive correlation between the ICR and the PICR for initial screens (r = 0.81), but less so for subsequent screens (r = 0.65).
  
  
  CONCLUSIONS
  This alternate measure seems to capture the burden of interval cancers just as well as the traditional PICR, without need for the increasingly difficult estimation of background incidence, making it a more accessible tool when evaluating mammography screening program performance.
authors.affiliation: Department of Public Health, University of Copenhagen, CSS, Øster Farimagsgade 5, 1014 Copenhagen K, Denmark. suban@sund.ku.dk.
authors.forename: Sune Bangsbøll
authors.initials: SB
authors.lastname: Andersen
authors.forename: Sven
authors.initials: S
authors.lastname: Törnberg
authors.forename: Elsebeth
authors.initials: E
authors.lastname: Lynge
authors.forename: My
authors.initials: M
authors.lastname: Von Euler-Chelpin
authors.forename: Sisse Helle
authors.initials: SH
authors.lastname: Njor
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology; D055088:Early Detection of Cancer / Q000379:methods*; D005260:Female; D006801:Humans; D015994:Incidence; D008327:Mammography / Q000379:methods; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D015397:Program Evaluation