title: Predicting the stage shift as a result of breast cancer screening in low- and middle-income countries: a proof of concept.
abstract: OBJECTIVE
  To provide proof of concept for a simple model to estimate the stage shift as a result of breast cancer screening in low- and middle-income countries (LMICs). Stage shift is an essential early detection indicator and an important proxy for the performance and possible further impact of screening programmes. Our model could help LIMCs to choose appropriate control strategies.
  
  
  METHODS
  We assessed our model concept in three steps. First, we calculated the proportional performance rates (i.e. index number Z) based on 16 screening rounds of the Nijmegen Screening Program (384,884 screened women). Second, we used linear regression to assess the association between Z and the amount of stage shift observed in the programme. Third, we hypothesized how Z could be used to estimate the stage shift as a result of breast cancer screening in LMICs.
  
  
  RESULTS
  Stage shifts can be estimated by the proportional performance rates (Zs) using linear regression. Zs calculated for each screening round are highly associated with the observed stage shifts in the Nijmegen Screening Program (Pearson's R: 0.798, R square: 0.637).
  
  
  CONCLUSIONS
  Our model can predict the stage shifts in the Nijmegen Screening Program, and could be applied to settings with different characteristics, although it should not be straightforwardly used to estimate the impact on mortality. Further research should investigate the extrapolation of our model to other settings. As stage shift is an essential screening performance indicator, our model could provide important information on the performance of breast cancer screening programmes that LMICs consider implementing.
authors.affiliation: Department of Primary and Community Care, Radboud university medical center, Nijmegen, The Netherlands Sten.Zelle@radboudumc.nl.
authors.forename: Sten G
authors.initials: SG
authors.lastname: Zelle
authors.affiliation: Department of Primary and Community Care, Radboud university medical center, Nijmegen, The Netherlands.
authors.forename: Rob
authors.initials: R
authors.lastname: Baltussen
authors.affiliation: Department for Health Evidence, Radboud university medical center, Nijmegen, The Netherlands.
authors.forename: Johannes D M
authors.initials: JD
authors.lastname: Otten
authors.affiliation: Department of Public Health, Erasmus Medical Centre, Rotterdam, The Netherlands.
authors.forename: Eveline A M
authors.initials: EA
authors.lastname: Heijnsdijk
authors.affiliation: Department of Primary and Community Care, Radboud university medical center, Nijmegen, The Netherlands.
authors.forename: Guido
authors.initials: G
authors.lastname: van Schoor
authors.affiliation: Department for Health Evidence, Radboud university medical center, Nijmegen, The Netherlands Dutch reference centre for screening, Nijmegen, The Netherlands.
authors.forename: Mireille J M
authors.initials: MJ
authors.lastname: Broeders
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000175:diagnosis / Q000453:epidemiology* / Q000473:pathology; D003906:Developing Countries; D055088:Early Detection of Cancer / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D016014:Linear Models; D008403:Mass Screening; D008875:Middle Aged; D008954:Models, Biological; D011203:Poverty; D055815:Young Adult
keywords: Breast cancer control; CBE screening; breast cancer screening; developing countries; model; stage distribution; validation