First results on mortality reduction in the UK Trial of Early Detection of Breast Cancer. UK Trial of Early Detection of Breast Cancer Group.

Between 1979 and 1981 the UK Trial of Early Detection of Breast Cancer enrolled women aged 45-64 living in eight locations in the United Kingdom. Annual screening by clinical examination of the breast, with mammography in alternate years, was provided over 7 years for 45,841 women; 63,636 were offered teaching in breast self-examination and were provided with a self-referral clinic; and 127,117, for whom no extra services were provided, form a comparison population. Over the 7 years from the start of the trial a reduction in the risk of dying from breast cancer in women offered screening relative to that in the comparison population was observed. The reduction was 14% (RR 0.86, 95% CI 0.69-1.08) when no allowance was made for underlying differences in breast cancer mortality between the populations, but rose to 20% (RR 0.80, 95% CI 0.64-1.01) when adjusted for differences in pretrial mortality rates. These differences fall short of statistical significance. No reduction in mortality was observed during the first 5 years but thereafter the gap widens. These results, though in themselves inconclusive, are consistent with the hypothesis that screening can achieve a worthwhile mortality reduction. No difference in mortality has so far been observed between women offered teaching in breast self-examination and the comparison population.