Reliability of estrogen receptors in predicting response to antiestrogens.

In postmenopausal women, about 65% to 80% of breast cancers contain estrogen receptors (ERs) and 50% to 65%, progesterone receptors (PRs). Receptor-positive breast cancer is somewhat less common in premenopausal patients. Recently, the biochemical dextran-coated charcoal (DCC) assay for ERs has been replaced in many laboratories by immunohistochemical and immunocytochemical methods, which are not disturbed by endogenous estrogen or antiestrogen treatment. Receptors now can also be assayed from fine-needle biopsy and paraffin-embedded tissue specimens. The ER has been shown to be a prognostic factor for overall and disease-free survival in newly diagnosed and relapsed breast cancer. The value of the ER in predicting response to both surgical and medical endocrine treatment of breast cancer has been demonstrated. Ample evidence supports the predictive value of the ER in the treatment of breast cancer with the antiestrogen tamoxifen (Nolvadex). The first studies of a new antiestrogen, toremifene (Fareston), support the value of the ER in predicting breast cancer treatment results.