ENDOGENOUS ESTROGEN AND POSTMENOPAUSAL BREAST-CANCER A QUANTITATIVE REVIEW

This paper systematically reviews the results from epidemiologic studi es investigating the hypothesis that breast cancer risk in postmenopau sal women increases with increasing concentrations of estradiol in blo od and with increasing urinary estrogen excretion rates. Data from 29 epidemiologic studies of endogenous hormones and postmenopausal breast cancer were used, The ratio of the average estrogen concentration in the women with breast cancer to that in the women without breast cance r (and its 95 percent confidence interval [CI] was calculated for each study, and the results were summarized by calculating weighted averag es of the log ratios. In six prospective studies of serum estradiol co ncentration, 329 women who subsequently developed breast cancer had, o verall, a 15 percent (CI = 6-24 percent, P= 0.0003) higher mean concen tration of estradiol in their blood than the 1,185 women who remained free of cancer. The results of these prospective studies did not diffe r significantly from each. other (chi(2) for heterogeneity = 8.7; degr ees of freedom = 5; P> 0.1). Similar differences in mean estrogen leve ls were seen in the case-control studies which reported either estradi ol concentrations in the blood or urinary estrogen excretion. However, the case-control studies showed significant heterogeneity among their results. The data from the prospective studies strongly suggest that breast cancer risk in postmenopausal women is associated with relative ly high concentrations of endogenous estradiol.