ABSTRACT
In the Edinburgh Breast Screening Project, 210 cancers were detected from commencement in 1979 up to December 1984. By this time the full initial cohort had completed at least three visits and a proportion had attended for up to five visits, so pathological characteristics for prevalent and incident cancers could be compared. The main differences were in distribution of histological type of cancer, detection of occult invasive disease, and lymph-node positivity among incident tumors. Only the first of these was statistically significant. This evaluation showed that cancer detection by screening in Edinburgh conformed with screening theory, in which detection of good prognosis tumors is favored at the prevalence screens, and faster growing, aggressive tumors are found at the incidence screens. Qualitative histopathology may provide a better measure than standard quantitative judgments of size and lymph node status to compare the varieties of cancer detected by screening programmes and to understand the biology of the disease.
