Beyond randomized controlled trials

The work by Tabár et al., published in a recent issue of Cancer,1 is a clear demonstration that mammographic screening can reduce the death rate from breast carcinoma dramatically in service screening and that the benefit is not confined just to randomized clinical trials. The decrease in mortality rates reported in the Swedish Two Counties follows a dose-response curve: the more women who are screened, the greater the mortality reduction. Having remained virtually unchanged over the previous 50 years, the death rate from breast carcinoma abruptly began to decrease in the U.S. in 1989. There has been considerable debate with regard to the reason for this decline.2 Many have attributed it to better therapy. Indeed, better therapy may be a component, but a review of the annual incidence rates of breast carcinoma in the U.S. provides more direct evidence that much of the decrease is due to screening. Data from the Connecticut tumor registry and the Surveillance, Epidemiology, and End Results (SEER) program3 demonstrate that the annual incidence of invasive breast carcinoma in the U.S. had increased steadily since 1940. The incidence rose annually from approximately 60 cases per 100,000 population to greater than 90 cases per 100,000 population in 1982. In 1983–1984, there was a sudden dramatic increase in the annual incidence of breast carcinoma and over the next several years this incidence continued to increase at a more rapid rate, reaching as high as 115 cases of breast carcinoma diagnosed per year. It soon became apparent that this increase was due to the earlier detection of tumors as a result of the onset of a much higher rate of mammographic screening4 due to the recognition of mortality reductions from the randomized controlled trials (RCT). Breast carcinoma was being detected earlier, adding to the baseline incidence that was present without screening. This abrupt upturn provides an objective marker for the onset of widespread mammographic screening in the U.S. Because periodic screening is more likely to detect tumors with moderate growth rates, the RCTs have demonstrated that a mortality reduction is likely to appear 5–7 years after the onset of screening. This is precisely the time frame after screening began in the U.S. in which the mortality rates began a sudden decrease in a trend that has continued. The evidence appears quite clear. Although mammographic screening is far from perfect, the benefits that were shown objectively in the RCTs currently are being demonstrated for populations outside trials. Although we must continue the effort to find ways to reduce the number of deaths from breast carcinoma further, mammographic screening is the most powerful tool currently available. Women should be encouraged to take advantage of the potentially life-saving benefits of screening. Daniel B. Kopans M.D.*, * Department of Radiology Harvard Medical School; Wang Ambulatory Care Center Massachusetts General Hospital Boston, Massachusetts