17-Year Follow-up Indicates Early but Not Overall Reduction in Breast Cancer Mortality With Annual Mammography Screening at Age 40-49 Years
The 17-year follow-up in the UK Age trial, reported in The Lancet Oncology by Moss et al, indicated a reduction in breast cancer mortality during the first 10 years after diagnosis but not thereafter among women invited for annual mammography screening from age 40 to 49 years compared with invitation to screening at age 50 and every 3 years thereafter. The previously reported 10-year follow-up had shown no difference in mortality between groups.
Study Details
In the trial, 160,921 women aged 39 to 41 years from 23 UK National Health Service Breast Screening Programme units were randomly assigned (1:2) between October 1990 and September 1997 to an intervention group offered annual screening by mammography up to and including the calendar year of their 48th birthday (n = 53,883) or a control group receiving usual medical care including invitation for screening at age 50 years and every 3 years thereafter (n = 106,953).
Mortality
After a median follow-up of 17 years, the rate ratio (RR) for breast cancer mortality from tumors diagnosed during the intervention phase was 0.88 (95% confidence interval [CI] = 0.74–1.04). The reduction in breast cancer mortality in the intervention group from tumors diagnosed during the intervention phase was significant in the first 10 years after diagnosis (RR = 0.75, 95% CI = 0.58–0.97) but not thereafter (RR = 1.02, 95% CI = 0.80–1.30). Including all follow-up, rates of breast cancer mortality per 1,000 women-years were 0.257 in the intervention group and 0.276 in the control group (RR = 0.93, 95% CI = 0.80–1.09).
The overall breast cancer incidence rates per 1,000 women-years were 2.06 in the intervention group and 2.09 in the control group (RR = 0.98, 95% CI = 0.93–1.04). RRs were 1.06 (95% CI = 0.91–1.23) for in situ cancers and 0.97 (95% CI = 0.92–1.03) for invasive cancers, yielding absolute differences of an additional 0.25 in situ cancers and 0.93 fewer invasive cancers per 1,000 women invited for annual screening.
The investigators concluded: “Our results support an early reduction in mortality from breast cancer with annual mammography screening in women aged 40-49 years. Further data are needed to fully understand long-term effects. Cumulative incidence figures suggest at worst a small amount of overdiagnosis.”
Sue Moss, PhD, of Wolfson Institute, Queen Mary University of London, is the corresponding author for the Lancet Oncology article.
The study was funded by the National Institute for Health Research Health Technology Assessment program and the American Cancer Society. Past funding was provided by the Medical Research Council, Cancer Research UK, the UK Department of Health, and the US National Cancer Institute.
For full disclosures of the study authors, visit www.thelancet.com/journals/lanonc.
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