Immunocytochemical assay for estrogen receptor: relationship to outcome of therapy in patients with advanced breast cancer.

We have used an immunoperoxidase technique utilizing a monoclonal antibody to the estradiol receptor to identify immunoreactive estradiol receptor in breast carcinomas and have examined the relationship between the immunoreactive estradiol receptor and response to therapy in patients with advanced breast cancer. Fifty-six patients were found to be assessable for response to endocrine therapy. Twenty-two showed an objective response to some form of endocrine manipulation, and all these had positively stained carcinomas. None of the 17 patients with negatively stained carcinomas responded to endocrine therapy. We conclude that the monoclonal antibody to estradiol receptor can help identify breast cancer patients who may respond to endocrine therapy.