A blind review and an informed review of interval breast cancer cases in the Limburg screening programme, the Netherlands

Objective To investigate the proportion of interval breast cancers that could have been detected at the previous screening examination, and to gain more insight into the characteristics of these tumours. Setting Breast cancer screening programme in mid- and southern Limburg, the Netherlands. Method Firstly, previous screening mammograms of 92 interval cancer cases were blindly reread by the radiologists from two different units as part of their daily screening workload. Secondly, a separate informed review was conducted, in which all of the cases (except for two) were subclassified into four categories: screening error; minimal signs; radiologically occult both at previous screening and at diagnosis; or radiologically occult at previous screening. Trends in recall rates and false and true positive rates were calculated to study potential changes during and after the blind review. Results In the blind review, 15% of the interval cancers were detected in both rereadings and 21% in one rereading. In the informed review, 25% were classified as a screening error and 24% as minimal signs present; 74% of the cases classified as a screening error had been recalled at least once in the blind review. Recall rates and false positive rates in daily screening practice increased significantly during and after the study period. Conclusions About one third of the interval cancers could have been detected in the previous screening round. In order to diminish the number of avoidable interval cancers, review and classification of interval cancers is an important tool for continuing the education of screening radiologists. Therefore, further development of review training procedures is necessary.