Breast cancer mortality after 10 years in the UK Trial of Early Detection of Breast Cancer

Abstract

The United Kingdom Trial of Early Detection of Breast Cancer is a population-based but non-randomized controlled trial of the effect on breast cancer mortality of two early detection strategies: a) screening in which mammography was provided at 24 month intervals in addition to annual physical (clinical) examination for a period of 7 years and b) education in breast self-examination (BSE). Women aged 45–64 at entry in two screening districts, two BSE districts and four comparison districts have been followed up for 10 years through flagging their records at the National Health Service Central Registries. The reduction in breast cancer mortality observed after 7 years in the screening districts has been sustained. The risk in the combined screening populations relative to the comparison populations is 0.80 (95% CI 0.67–0.95) after adjustment for pre-trial breast cancer mortality. No reduction is seen in the BSE centres when viewed together but there is a considerable and unexpected difference between the two. Analysis by age at entry suggests that women aged 45–49 at entry experienced a similar benefit to older women though the power of the study to detect age-specific differences is weak. It was not possible to adjust for all the factors other than the early detection interventions which may have contributed to differences in breast cancer mortality. The non-randomized design of the study has thus proved to be a serious impediment to interpretation of the results but the study continues to provide support for the view that screening can reduce breast cancer mortality by about 20% in the age-group now targeted by the UK national screening programme. Any benefit of teaching BSE remains unproven.