Background. We conducted an analysis of prospectively collected data to compare the clinical behavior of ER-negative versus ER-positive tumors with respect to rates and sites of recurrence.

Methods. A total of 647 patients with operable stage II or III breast cancer were enrolled in two consecutive adjuvant therapy protocols conducted between 1980 and 1986. The correlations between ER status and time to first recurrence, site of first recurrence, and time to breast cancer death were assessed on 558 (86%) patients with available ER status data using hazard function and hazard ratio function analysis.

Results. The rates of recurrence were significantly higher in patients with ER-negative status for the first two years of follow-up, but not thereafter. Similar results were observed for breast cancer death, and these results held up after adjustment for differences in treatment, age, menopausal status, and tumor burden. When the site of first recurrence was studied, ER-negative status was associated with a significantly higher rate of tumor recurrence in the viscera and soft tissues, while ER-positive status was associated with significantly higher rates of tumor recurrence involving bone.

Conclusions. The clinical behavior of ER-positive tumors is different from ER-negative cancer. ER status had a pronounced effect on the rates and sites of recurrence. Furthermore, this apparent association diminished over the follow-up period. Recurrence rates were significantly higher in patients with ER-negative status for the first two years of follow-up, but not thereafter.