FOLLOW-UP AFTER 11 YEARS - UPDATE OF MORTALITY RESULTS IN THE STOCKHOLM MAMMOGRAPHIC SCREENING TRIAL

Results from several randomised mammography screening trials have show n that it is possible to reduce mortality in breast cancer by mammogra phic screening at least for women above 50 years of age. The purpose o f this article is to present data on mortality in breast cancer in stu dy and control groups of the Stockholm trial after 11 years of followu p, to analyse which age group benefits most from screening. In March 1 981, 40, 318 women in Stockholm, aged 40 through 64 years, entered a r andomized trial of breast cancer screening by single view mammography alone, versus no intervention in a control group of 20 000 women. Two screening rounds were performed and the attendance rate was over 80% i n the two rounds. During 1986 the control group was invited once to sc reening. Totally 428 and 217 cases of breast cancer were diagnosed in the study and control groups respectively. After a mean follow-up of 1 1.4 years a nonsignificant mortality reduction of 26% was observed for the whole study group, with a relative risk (RR) of death in breast c ancer of 0.74 (CI(confidence interval) = 0.5-1.1). For women aged 50-6 4 years a significant 38% mortality reduction was observed with a RR o f 0.62 (CI = 0.38-1.0). For women aged 40-49 years no effect on mortal ity was found, with a RR of death in breast cancer of 1.08 (CI = 0.54- 2.17). The breakpoint for benefit in this study seemed to be at 50 yea rs of age when 5-year age groups were analysed, but this tendency is u ncertain because of the low statistical power in the analysis of the y ounger age groups. Long screening intervals, the use of single-view ma mmography, and the fact that more than 50% of the women in age group 4 0-49 years were still below 50 years of age when the study was closed, were all facts that could have influenced the results in age group 40 -49 years. Larger studies are needed to answer the question whether ma mmographic screening can be successful in younger age groups.