Recombinant cell ultrasensitive bioassay for measurement of estrogens in postmenopausal women.

A recent analysis of data from nine studies provided convincing evidence that plasma estradiol measurements predict the risk of breast cancer in normal postmenopausal women. However, the median values detected by the various assays used in this study varied by 5-fold. These and other published data in normal postmenopausal women suggest that assays measuring low plasma estradiol concentrations suffer from problems of sensitivity, specificity, and precision.