Population surveys have demonstrated an inverse relationship between breast cancer incidence rates and the urine “estriol ratio,” the concentration of estriol relative to the sum of the concentrations of estrone and estradiol. In this study, the urine estriol ratio was evaluated in premenopausal breast cancer patients and control women from Boston and San Francisco. Although at least 2 years had passed since last use of oral contraceptives, women with a history of oral contraceptive use for 19 months or longer excreted estrogen in low concentrations compared to nonusers and so were excluded. Among the remaining 73 cases and 55 controls, the cases had lower estriol ratios and higher estrone and estradiol levels than did controls. However, these differences, which averaged about 10%, were not statistically significant. Thus the hypothesis that a low estriol ratio is a cause of breast cancer is given only minimal support. Among women in their 40's, the excretion of estrogens is subject to many influences and is difficult to study. The many determinants of estrogen excretion, including age and oral contraceptive use, should be accommodated in the design of future studies of the estriol ratio.

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Supported by a Specialized-Center Grant (5 PO1 CA06373) from the National Cancer Institute and a research grant from the American Cancer Society (ET-58A).

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