Estrogen receptor and natural course of breast cancer.

The tumors from approximately 50% of patients with breast cancer contained estrogen receptor (ER). ER appeared more often and at higher levels in the tumors of postmenopausal women. Eleven out of 12 patients who had multiple ER assays from various metastatic sites showed no significant discrepancies in ER values. ER level appears to decrease as the duration of metastatic cancer increase. Patients with ER in the tumor more frequently have bone metastases than those without ER. Visceral metastases occurred more often with ER negative patients and appeared to have a more malignant course with significant shorter survival.