Stage distribution at first and repeat examinations in breast cancer screening

Objectives To investigate observed stage distributions at first and repeat screenings. To compare the observed outcomes with expected values based on simulation modelling, varying the assumptions about the natural history of the disease. Methods-An overview is made of observed data on stage distribution at first and repeat screenings and the difference between those distributions is su mmarised in a Gini coefficient. Four possible explanations for the observat ions are considered, two of these are worked out as Miscan simulation model s, and the outcomes are compared with observations. Results-Often the reported stage distributions at repeat screenings are not or only slightly more favourable than at first screenings and, in the ones that are more favourable, the difference is relatively small. If, in the M iscan model,it is assumed that there is no correlation between the duration of preclinical breast cancer in consecutive tumour size categories and tha t there is a strong influence of latent cancers, it is not possible to repr oduce the observed outcomes. Conclusions-The two modelled explanations are not sufficient. Decreasing se nsitivity seems an unlikely explanation for the discrepancy in many screeni ng programmes. The possibility that the observations may be explained becau se false reassurance has been given should be seriously considered and inve stigated.