The visibility of cancer on earlier mammograms in a population-based screening programme

The aim of this study was to examine how frequently the later-round screen- detected and interval breast cancers were visible in earlier screening mamm ograms by retrospective review and to compare their radiological and clinic opathological features with those diagnosed by primary screening. In a popu lation-based mammography screening programme 63 731 women aged 50-59 years were invited and 56158 examinations were carried out in the period 1987-199 2 in the Tampere area in Finland. A total of 276 breast cancers were detect ed, of which 131 were diagnosed on later screening rounds or were interval cancers. A retrospective review of previous screening mammograms was carrie d out in 130 cases by the radiologist who diagnosed the breast cancer and t hus knew the exact location of the tumour, no blinded review was carried ou t. 43 (33%) cancers were visible, 84 (65%) were not visible and 3 (2%) not included on the mammogram in a retrospective review. Later round screen-det ected cancers were statistically significantly more often visible in earlie r screening mammograms (43%) than interval cancers (19%) (P = 0.002). Tumou rs missed by screening mammography but which were visible on retrospective review were often histologically well-differentiated and were more often di agnosed in the subsequent screening round than by clinical diagnosis as int erval cancers. If all retrospectively visible interval cancers had been dia gnosed by screening 19% (10/54) of the interval cancers could have been avo ided. If all retrospectively visible cancers had been diagnosed at the time of false-negative screening or assessment 65% (84/130) of all patients wou ld have benefitted from an earlier diagnosis compared with the actual figur e of 31% (41/130). (C) 1999 Elsevier Science Ltd. All rights reserved.