Estrogen receptor (ER) antagonists have been widely used for breast cancer treatment, but the efficacy and drug resistance remain to be clinical concerns. The purpose of this Study was to determine whether the extracts of coptis, an anti-inflammatory herb, improve the anticancer efficacy of ER antagonists. The results showed that the combined treatment of ER antagonists and the crude extract of coptis or its purified compound berberine conferred synergistic growth inhibitory effect on MCF-7 cells (ER+), but not On MDA-MB-231 cells (ER-). Similar results were observed in the combined treatment of fulvestrant, a specific aromatase antagonist. Analysis of the expression of breast cancer related genes indicated that EGFR, HER2. bcl-2, and COX-2 were significantly downregulated, while IFN-beta and p21 were remarkably upregulated by berberine. Our results Suggest that coptis extracts could be promising adjuvant to ER antagonists in ER positive breast cancer treatment through regulating expression Of Multiple genes. (C) 2008 Elsevier Inc. All rights reserved.