Effect of Screening and Adjuvant Therapy on Mortality From Breast Cancer

In several countries, a drop in mortality from breast cancer has been documented starting in 1975. Both early detection by mammographic screening and advances in management are plausible explanations. The National Institutes of Health have used a competitive peer review process to develop 7 independent statistical models of breast cancer incidence and mortality. A consortium of investigators used the same sources to obtain data on screening mammography, adjuvant treatment, and health benefits relating to the rate of death from breast cancer in the years 1975–2000. The use of mammographic screening in women age 40 and over increased markedly over the period 1985 to 2000. The use of adjuvant treatment depended on numerous factors beside the calendar year, including age, tumor stage, and estrogen-receptor status. The proportion of women given adjuvant treatment increased from virtually none in 1975 to approximately 80% in 2000. By 2000, half of all women were using tamoxifen. All 7 models predicted similar proportional reductions in mortality from a combination of screening and adjuvant therapy. The proportion of overall reduction in breast cancer deaths ascribed to screening ranged from 28% to 65% (median, 46%). The remaining decrease in mortality was associated with adjuvant treatment. Variation between models in the absolute contribution of screening was greater than for treatment. Combined screening and adjuvant therapy reduced breast cancer mortality by 25 to 38% (median, 30%). The proportion of decreased mortality ascribed to adjuvant treatment was 12 to 21% (median, 19%). For each of the 7 models, the combination of screening and adjuvant treatment lowered mortality slightly less than the sum of contributions from screening and adjuvant therapy alone. The investigators conclude from these findings that both mammographic screening and adjuvant treatment have helped to lower deaths from breast cancer in the United States.