Plasma levels of estrone, estrone sulfate, and estradiol and the percentage of unbound estradiol in postmenopausal women with and without breast disease.

To investigate the possibility of increased tissue exposure to estrogen in breast cancer patients, plasma levels of estrogens and the percentage of unbound estradiol were measured in postmenopausal women with benign or malignant breast disease and compared with levels in normal postmenopausal women. The percentage of unbound estradiol in breast cancer patients [1.85 +/- 0.35% (S.D.)] was significantly higher (p less than 0.001) than in normal postmenopausal women [1.52 +/- 0.33%] and was still significantly higher when patients were matched with control subjects for weight (p less than 0.001) or ideal body weight (p less than 0.001). The binding capacity of sex hormone binding globulin was similar in both groups of women. No significant differences in the plasma levels of estrone, estradiol, or estrone sulfate were detected between breast cancer and normal subjects. It is concluded that, given similar concentrations of estradiol in plasma of normal and breast cancer subjects, the significant increase found in the unbound estradiol fraction may result in a very small increment in tissue exposure to estrogens in breast cancer subjects. However, even such a small increase in tissue exposure to estradiol may be significant, given the length of time required for breast tumor development.