Measures of benefit for breast screening from the pathology database for Scotland, 1991-2001

To examine pathology characteristics of breast cancers detected by mammography screening over 10 years in Scotland, and compare the nature of cancer yields after different levels of very small invasive cancer at prevalence detection.

A pathology database of cancers from mammography screening of women aged 50-64 years invited every three years was used to assess the variation over time in annual yield of different invasive cancer sizes. Screening centres were compared for incidence screen yields, according to sizes, histological type, grade, and node status.

There was a significant trend over time for increased detection of < 15 mm cancers among 2353 prevalence cancers, and a significant trend for increase in all size groups, < 10, 10-14, < 15, and >or= 15 mm, among 2245 incidence cancers. Based on individual screening centres, there was a significant negative relation between proportions of very small (< 10 mm) cancers at prevalence screens and of large (>or= 15 mm) cancers at incidence screens of the same "cohort" three years later. There was no significant relation on the same centre basis for worse pathology characteristics (histological no special type, high grade, and positive node status) in cancers detected in the same "cohort" three years later.

Sensitive mammography screening has a significant effect on the nature of yields at subsequent screens. Length of screening interval and consistency in pathologist opinions are factors that account for lack of effect on incidence cancer qualitative pathology characteristics. These issues are relevant to the use of such characteristics as surrogate measures of service screening performance.