Mammographic and pathological features of breast cancer detected at first incident round screening

This study investigated the proportion of first incident screen detected cancers diagnosable at prevalent round. The prevalent mammogram was classified as truly negative (no abnormality) or falsely negative (cancer diagnosable) after blinded review. Of 54 incident cancers, 63% were true and 26% false negatives. Five cancers were assessed at the prevalent round but dismissed as normal. The possible consequence of delayed diagnosis was inferred from the pathological prognostic indicators and calculated Nottingham prognostic index of the incident tumours, and comparison with prevalent screen, symptomatic and interval cancers. Compared to the true negatives, a significantly greater proportion of false negative incident tumours were in the very good prognostic group, i.e. in many of the latter the prognosis is probably unaffected, although in part this is because a number of the fast growing false negative tumours will result in interval cancers. Significantly fewer incident tumours were of good prognosis compared to the prevalent round, possibly an adverse affect of 3-yearly screening. Parenchymal deformities and calcifications were the most frequent false negative mammography signs and appear to represent good prognosis lesions.