Breast cancers missed in the prevalent screening round: effect upon the size distribution of incident round detected cancers

Objective-To determine the effect of false negative screens (missed cancers ) in the prevalent screening round on the relative size distribution of can cers detected at the first incident screen. Setting-The Bolton, Bury, and Rochdale breast screening programme. Methods-One hundred and three breast cancers detected in the first incident round of screening were analysed. The previous (prevalent round) screening films taken between two and four years earlier were subjected to blinded r eview and classified as either true negatives (no significant abnormality v isible) or false negatives (a suspicious abnormality visible at the site of the subsequently detected cancer). The pathological size, type, and grade (where appropriate) of the cancers were recorded Results-Fifty one of the 103 cancers (49%) detected in the first incident r ound screen measured <15 mm in diameter. A total of 32 cases were classifie d as false negatives. Of these, 12 (38%) measured <15 mm in diameter. If al l the false negative cancers had been detected at the prevalent screen, 39 (55%) of the remaining 71 cancers detected in the first incident round scre en would have measured <15 mm. A relative excess of lobular carcinomas was found among the false negatives. Conclusions-The findings suggest that although false negative screens in th e prevalent round increase the number of cancers available for detection at the first incident round screen, many of these cancers are still. <15 mm i n diameter at detection. Cancer detection performance in the prevalent scre ening round has only a minor influence on the relative proportion of small and large cancers detected at the first incident round screen.