Early detection and improved treatment have contributed almost equally to the substantial decrease i

Early detection through screening mammography and improved adjuvant treatment have contributed almost equally to the substantial decrease in breast cancer death rates over the past 10 to 15 years, researchers conclude in an unprecedented effort to parse out the factors that have led to the decline.

The study, published in the Oct. 27 issue of the New England Journal of Medicine, was supported by the National Cancer Institute (NCI) and conducted by seven research groups, including The University of Texas M. D. Anderson Cancer Center.

Researchers sought to end the longstanding controversy of whether screening mammography, better treatment or a combination of the two is responsible for improved Breast cancer survival.

The seven teams consisting of 43 investigators designed their own statistical models to determine the contribution of each method. These independent models used the same sources of data, some of which had not been mined before, but their approaches and assumptions differed.

The teams reached somewhat different conclusions, but were closest to each other in estimating how much the adjuvant therapies tamoxifen and chemotherapy reduced mortality in patients (12 percent to 21 percent, with a median of 19 percent). The range for screening mammography, however, was 7 percent to 23 percent (with a median of 15 percent), reflecting the greater uncertainty associated with estimating the benefit of screening.

Still, according to the models, the combination of screening and adjuvant therapy together reduced the Breast cancer death rate by an estimated 25 percent to 38 percent, with a median of 30 percent - which explains the drop in Breast cancer mortality from 1975 to 2000, says the study's lead author, Donald Berry, Ph.D., chair of the Department of Biostatistics and Applied Mathematics at M. D. Anderson Cancer Center.

"While we didn't agree with each other as to the percentages of benefit, all seven groups concluded that the decline in the rate of death from Breast cancer is a combination of screening and therapy and not restricted to one or the other," he says. "Screening would have no benefit if not followed by treatment, including surgery, and treatment has the potential to be more effective if cancer is detected at earlier stages by screening."

Berry stresses that the differences in conclusions reflect uncertainties in the interpretation of available information and differing modeling approaches, rather than contradictions among the models. "These are seven top modeling groups applying their efforts to the best data that we have available in this country," he says.