Second round cancers: how many were visible on the first round of the UK National Breast Screening Programme, three years earlier?

The first round screening films of 100 women who had cancers detected in the second round of the NHS Breast Screening Programme, were reviewed blindly, and then retrospectively, with knowledge of the site of the subsequent cancer. On initial blind viewing of the first screening mammograms, a lesion, later histologically proven to be the cancer, was correctly identified in 25 false-negative lesions. However, 51 false positive lesions which did not develop into cancer were also identified. Review with knowledge of the site of the lesions at second round screening identified an additional 19 false negative lesions. The mammographic features of the 25 false negative lesions initially identified on blind review were ill-defined masses (52%), architectural distortion (20%), asymmetrical densities (16%), enlarged lymph nodes (8%) and a well defined lesion (4%). Sixteen of these lesions were classified as minimal change, suspicious change in four, clearly malignant in three and benign in two. Forty-eight percent of the false negative lesions occurred in the established review areas of the breast. On retrospective review, 25% of incident round screen detected breast cancers were potentially detectable on the previous screening mammograms and the majority of these lesions were ill-defined masses that were more likely to occur in the 'review areas' of the breast. However, only 7% demonstrated mammographic features that were clearly recognized as suspicious of malignancy. We therefore recommend that radiologists involved in screen reading should pay particular attention to abnormalities occurring in the so-called review areas.