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 cou ld have been detected at the previous screening examination, and to gain mo re 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 w ere blindly reread by the radiologists from two different units as part of their daily screening workload. Secondly, a separate informed review was co nducted, in which all of the cases (except for two) were subclassified into four categories: screening error; minimal signs; radiologically occult bot h at previous screening and at diagnosis; or radiologically occult at previ ous screening. Trends in recall rates and false and true positive rates wer e calculated to study potential changes during and after the blind review. Results-In the blind review, 15% of the interval cancers were detected in b oth rereadings and 21% in one rereading. In the informed review, 25% were c lassified 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 t he blind review. Recall rates and false positive rates in daily screening p ractice increased significantly during and after the study period. Conclusions-About one third of the interval cancers could have been detecte d in the previous screening round. In order to diminish the number of avoid able interval cancers, review and classification of interval cancers is an important tool for continuing the education of screening radiologists. Ther efore, further development of review training procedures is necessary.