title: Effectiveness of early detection on breast cancer mortality reduction in Catalonia (Spain).
abstract: BACKGROUND
  At present, it is complicated to use screening trials to determine the optimal age intervals and periodicities of breast cancer early detection. Mathematical models are an alternative that has been widely used. The aim of this study was to estimate the effect of different breast cancer early detection strategies in Catalonia (Spain), in terms of breast cancer mortality reduction (MR) and years of life gained (YLG), using the stochastic models developed by Lee and Zelen (LZ).
  
  
  METHODS
  We used the LZ model to estimate the cumulative probability of death for a cohort exposed to different screening strategies after T years of follow-up. We also obtained the cumulative probability of death for a cohort with no screening. These probabilities were used to estimate the possible breast cancer MR and YLG by age, period and cohort of birth. The inputs of the model were: incidence of, mortality from and survival after breast cancer, mortality from other causes, distribution of breast cancer stages at diagnosis and sensitivity of mammography. The outputs were relative breast cancer MR and YLG.
  
  
  RESULTS
  Relative breast cancer MR varied from 20% for biennial exams in the 50 to 69 age interval to 30% for annual exams in the 40 to 74 age interval. When strategies differ in periodicity but not in the age interval of exams, biennial screening achieved almost 80% of the annual screening MR. In contrast to MR, the effect on YLG of extending screening from 69 to 74 years of age was smaller than the effect of extending the screening from 50 to 45 or 40 years.
  
  
  CONCLUSIONS
  In this study we have obtained a measure of the effect of breast cancer screening in terms of mortality and years of life gained. The Lee and Zelen mathematical models have been very useful for assessing the impact of different modalities of early detection on MR and YLG in Catalonia (Spain).
authors.affiliation: Biomedical Research Institut of Lleida (IRBLLEIDA), Lleida, Catalonia, Spain. montse.rue@cmb.udl.cat
authors.forename: Montserrat
authors.initials: M
authors.lastname: Rue
authors.forename: Ester
authors.initials: E
authors.lastname: Vilaprinyo
authors.forename: Sandra
authors.initials: S
authors.lastname: Lee
authors.forename: Montserrat
authors.initials: M
authors.lastname: Martinez-Alonso
authors.forename: Misericor-Dia
authors.initials: MD
authors.lastname: Carles
authors.forename: Rafael
authors.initials: R
authors.lastname: Marcos-Gragera
authors.forename: Roger
authors.initials: R
authors.lastname: Pla
authors.forename: Josep-Alfons
authors.initials: JA
authors.lastname: Espinas
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000401:mortality*; D015331:Cohort Studies; D055088:Early Detection of Cancer; D005260:Female; D006801:Humans; D008403:Mass Screening; D008875:Middle Aged; D015233:Models, Statistical; D013030:Spain