title: Interval cancers in the NHS breast cancer screening programme in England, Wales and Northern Ireland.
abstract: BACKGROUND
  The United Kingdom NHS Breast Screening Programme was established in 1988, and women aged between 50 and 70 are routinely invited at three yearly intervals. Expected United Kingdom interval cancer rates have been calculated previously, but this is the first publication from an exercise to collate individual-based interval cancer data at a national level.
  
  
  METHODS
  Interval cancer case ascertainment is achieved by the regular exchange of data between Regional Breast Screening Quality Assurance Reference Centres and Cancer Registries. The present analysis includes interval cancers identified in women screened between 1st April 1997 and 31st March 2003, who were aged between 50 and 64 at the time of their last routine screen.
  
  
  RESULTS
  In the periods >0-<12 months, 12-<24 months and 24-<36 months after a negative screen, we found overall interval cancer rates and regional ranges of 0.55 (0.43-0.76), 1.13 (0.92-1.47) and 1.22 (0.93-1.57) per 1000 women screened, respectively. Rates in the period 33-<36 months showed a decline, possibly associated with early re-screening or delayed presentation.
  
  
  CONCLUSIONS
  Interval cancer rates were higher than the expected rates in the 24-month period after a negative screen, but were similar to published results from other countries. Increases in background incidence may mean that the expected rates are underestimated. It is also possible that, as a result of incomplete case ascertainment, interval cancers rates were underestimated in some regions in which rates were less than the expected.
authors.affiliation: Cancer Screening Evaluation Unit, Institute of Cancer Research, 15 Cotswold Road, Sutton, Surrey SM2 5 NG, UK. Rachel.Bennett@icr.ac.uk
authors.forename: R L
authors.initials: RL
authors.lastname: Bennett
authors.forename: S J
authors.initials: SJ
authors.lastname: Sellars
authors.forename: S M
authors.initials: SM
authors.lastname: Moss
mesh_terms: D000368:Aged; D000465:Algorithms; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology; D002277:Carcinoma / Q000175:diagnosis* / Q000453:epidemiology; D057210:Delayed Diagnosis / Q000706:statistics & numerical data; D055088:Early Detection of Cancer / Q000379:methods / Q000592:standards*; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008327:Mammography / Q000592:standards / Q000706:statistics & numerical data; D008875:Middle Aged; D009660:Northern Ireland / Q000453:epidemiology; D010507:Periodicity; D015397:Program Evaluation; D012042:Registries; D013997:Time Factors; D014852:Wales / Q000453:epidemiology