Low biologic aggressiveness in breast cancer in women using hormone replacement therapy.

Abstract

The results indicate that breast cancer in women who receive HRT is biologically less aggressive than those without previous HRT. The lower cell-proliferation rate and smaller tumor size found in ER-positive tumors from current HRT users suggest a direct ER-mediated growth inhibitory effect of HRT on established breast tumors. This may at least partly explain why breast cancer in HRT users has a more favorable clinical course.