Mammographic screening for breast cancer demonstrably lowers mortality in women aged 50 years and older. Its efficacy for younger women is less certain, although some randomized trials do suggest benefit. Meta-analysis of previous trials has indicated a 15% drop in mortality for women 40 to 49 years of age, but this could partly be due to the inclusion of older women. The Age trial enrolled 160,921 women 39 to 41 years of age and randomly assigned them, in a 1:2 ratio, to have annual mammography up to age 48 years or to usual medical care. The results of the trial—carried out at 23 breast-screening units in the United Kingdom—were analyzed by the intention-to-treat method. Mortality rates for the two groups were compared after a mean follow-up interval of 10.7 years.
Just over 80% of women attended at least one routine screen, and the number of screens for these women averaged 5.6. A nonsignificant 17% reduction in breast cancer mortality was documented in the intervention group compared to control women. The relative risk (RR) was 0.83, and the 95% confidence interval (CI), 0.66–1.04. The absolute risk reduction was 0.40 per 1000 women asked to be screened (95% CI, 0.07–0.87). When adjusting for noncompliance in screened women, mortality was reduced 24% (RR, 0.76; 95% CI, 0.51–1.01). The number of women needed to screen to prevent one death in 10 years was estimated to be 2512, a figure equivalent to approximately 17,600 invitations to be screened.
The Age trial failed to demonstrate significantly reduced breast cancer mortality in women 40 to 48 years of age who were offered annual mammographic screening. It is planned to again analyze mortality rates after an average follow-up of 14 years. At present, women should be fully informed about possible unwanted effects of screening as well as the possible benefit, and also about procedural costs.
Cancer Screening Evaluation Unit, Institute of Cancer Research, Sutton, United Kingdom; Reproductive Epidemiology, University of Leeds, Leeds, UK; Nottingham Breast Institute, City Hospital, Nottingham, UK; and Department of Histopathology, Addenbrookes Hospital, Cambridge, UK