RESUMO
The rate of response of human breast cancer to endocrine therapy depends upon the estrogen receptor ER levels and progesterone receptor PR levels in tumor tissue. About 55% to 60% of all breast cancers have positive estrogen receptors. Higher values of ER are observed in postmenopausal women compared to younger women, and about 45% to 55% of metastatic breast tumors have positive estrogen receptor values. Approximately 60% of ER positive tumors will respond objectively to endocrine therapy, and about 80% of ER positive and PR positive tumors will respond to hormone therapy. Absence of ER in breast tumors seems to correlate well with the increased response to chemotherapy of the patients. The observation that patients whose tumors contained higher ER values, had longer disease free survival than patients with ER negative tumors, led to the use of ER and PR as the prognostic indicators of the disease. Thus, measurement of ER and PR in tumor biopsies gives us important information concerning future treatment and prognosis of the disease.
