title: Measuring the burden of interval cancers in long-standing screening mammography programmes.
abstract: OBJECTIVE
  Mammography screening programme sensitivity is evaluated by comparing the interval cancer rate (ICR) with the expected breast cancer incidence without screening, ie. the proportional interval cancer rate (PICR). The PICR is usually found by extrapolating pre-screening incidence rates, whereas ICR is calculated from data available in the screening programmes. As there is no consensus regarding estimation of background incidence, we seek to validate the ICR measure against the PICR.
  
  
  METHODS
  Screening data from the three mammography screening programmes of Stockholm, Copenhagen, and Funen in the period 1989-2011 provided data to calculate the ICR. The most commonly described methods of extrapolating pre-screening incidence rates to calculate the PICR were illustrated and PICRs were calculated by year and programme using these different methods and compared with the ICRs.
  
  
  RESULTS
  PICRs varied greatly, reaching a difference of 32-34% in Stockholm, 79% in Copenhagen, and 100-106% in Funen between the highest and the lowest value, depending on which method was applied. PICRs exhibited large variations yearly and from programme to programme. ICRs did not vary to the same extent, ranging on average from 0.100 to 0.136 in the first 12-months and between 0.201 and 0.225 in the last 12-months of the two-year period after a negative screen across the three programmes.
  
  
  CONCLUSIONS
  The value of the PICR is hugely influenced by which method is applied, whereas the ICR is calculated purely on data available within programmes. We find that the PICR, the establishing indicator for sensitivity, could preferably be replaced by the ICR.
authors.affiliation: Department of Public Health, University of Copenhagen, Denmark suban@sund.ku.dk.
authors.forename: Sune Bangsbøll
authors.initials: SB
authors.lastname: Andersen
authors.affiliation: Regional Cancer Center Stockholm - Gotland, Sweden.
authors.forename: Sven
authors.initials: S
authors.lastname: Törnberg
authors.affiliation: Regional Cancer Center Stockholm - Gotland, Sweden.
authors.forename: Sini
authors.initials: S
authors.lastname: Kilpeläinen
authors.affiliation: Department of Public Health, University of Copenhagen, Denmark.
authors.forename: Elsebeth
authors.initials: E
authors.lastname: Lynge
authors.affiliation: Department of Public Health, University of Copenhagen, Denmark.
authors.forename: Sisse Helle
authors.initials: SH
authors.lastname: Njor
authors.affiliation: Department of Public Health, University of Copenhagen, Denmark.
authors.forename: My
authors.initials: M
authors.lastname: Von Euler-Chelpin
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis; 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
keywords: Mammography; interval cancer; programme evaluation; screening; sensitivity