The Edinburgh Randomized Trial of Breast Cancer Screening

This article presents additional follow-up analysis of women aged 45-49 from the Edinburgh Randomized Trial of Breast Cancer Screening. The screening protocol included four mammographic examinations at two-year intervals and seven annual clinical examinations. Altogether, 21,774 women aged 45-49 were recruited from 1978 to 1985 using cluster randomization. After 10-14 years of follow-up, breast cancer mortality has been reduced by 12% to 18% (rate ratios, with and without adjustment for socio-economic status, are 0.88 and 0.82 respectively, with 95% confidence intervals CIs of 0.55-1.41 and 0.51-1.32). These benefits are smaller than that reported previously with shorter follow-up. This article also presents data from an observational study that compared survival beyond baseline (50-52 years) of women first offered screening before and after age 50. Based on six-year data, the results suggest that earlier screening confers follow-up benefit (hazard ratio for later screening = 1.60; 95% CI: 0.96-2.67), but these findings are not statistically significant. The trial is too small to yield statistically significant results by itself, but can make useful contributions to overview and meta-analyses.