Clinical impact of introduction of mammography screening in a non-screening country with special reference to the Copenhagen service mammography screening programme.

Abstract

As stated in the European guidelines for quality assurance in mammography screening, the objective of screening for breast cancer is to reduce morbidity and mortality from the disease without adversely affecting the health status of those who participate in screening (1). The effectiveness of a programme therefore relies on the quality, organisation, and population acceptability. When organising a screening programme, baseline epidemiological data is a prerequisite upon which the outcome measures of mammography screening must be compared, since a more favourable stage distribution in screen-detected cancers compared to clinically diagnosed cancers forms the basis of the mortality reduction (2). It has repeatedly been shown that tumour stage correlates with survival in breast cancer (3, 4). An early predictor of the effect of screening on breast cancer mortality is therefore an indubitable increase in early stage breast cancer incidence with the onset of screening, and a subsequent decrease in more advanced stage breast cancer incidence (5). The obtained change in stage distribution brought about by screening should also result in a higher degree of breast conserving therapy and a decrease in need of adjuvant treatment (6). Among the adverse effects of screening is the risk of a false positive mammography leading to a certain number of healthy women recalled for further assessment, and, further, the risk of overdiagnosis with mammographic detection of small, indolent malignancies, that might not have surfaced clinically in the absence of screening. In order to monitor the effects of a screening programme the European guidelines have set up performance indicators stating acceptable levels for the quality of the screening process, and early surrogate indicators by which the impact of a breast cancer screening programme can be assessed (1). These indicators are used as surrogate measures of the likelihood of achieving a subsequent mortality reduction (7). This review focuses on the clinical impact of introduction of mammography screening, exemplified by comparison of tumour stage and treatment of breast cancer detected by mammography screening with clinically detected breast cancers.