A case-control study to estimate the impact on breast cancer death of the breast screening programme in Wales

Objectives: The aim of this study was to estimate the effect of service screening, as provided by the NHS breast screening programme, on breast cancer mortality in Wales. Furthermore, we wished to ascertain whether a reduction in breast cancer mortality consistent with that observed in the randomised screening trials was being achieved. Setting: The NHS Breast Screening Programme in Wales, managed by Breast Test Wales, with headquarters in Cardiff. Methods: A case-control study design with 1:2 matching. The cases were deaths from breast cancer in women aged 50-75 years at diagnosis who were diagnosed after the instigation of screening in 1991 and who died after 1998. The controls were women who had not died of breast cancer or any other condition during the study period. One was from the same GP practice and the other from a different GP practice within the some district, matched by year of birth. Results: Based on 419 cases, the odds ratio for risk of death from breast cancer for women who have attended at least one routine screen compared to those never screened was 0.62 (95% confidence interval [CI] 0.47-0.82, p=0.001). After excluding cases diagnosed prior to 1995 and adjusting for self-selection bias, the estimated mortality reduction was 25% (odds ratio=0.75, 95% CI 0.49-1.14, P=0.09). Conclusion: The Breast Test Wales screening programme is achieving a reduction in breast cancer mortality of 25% in women attending for screening, which is consistent with the results of the randomized controlled trials of mammographic screening.