Estrogen receptors and response to endocrine therapy and cytotoxic chemotherapy in advanced breast cancer.

In a consecutive series of 191 patients with advanced breast cancer, the response rate to endocrine treatment was 46/136 (34%) in estrogen receptor positive (ER+) patients, compared with 5/55 (9%) in estrogen receptor negative (ER-) patients (P < 0.01). In a retrospective analysis of 47 patients, the response rate to cytotoxic chemotherapy was 20/33 (62%) for ER+ tumors and 8/14 (57%) for ER-. It is concluded that ER+ tumors have a significantly higher chance of responding to endocrine therapy than do ER- tumors, but that receptor status is not a determinant of response to cytotoxic chemotherapy.