Estrogen receptor beta expression is associated with tamoxifen response in ER alpha-negative breast carcinoma

Purpose: Endocrine therapies, such as tamoxifen are commonly given to most patients with estrogen receptor (ER) alpha-positive breast carcinoma but are not indicated for persons with ERalpha-negative cancer. The factors responsible for response to tamoxifen in 5-10% of patients with ERalpha-negative tumors are not clear. The aim of the present study was to elucidate the biology and role of the second ER, ERbeta, in patients treated with adjuvant tamoxifen. Experimental Design: We investigated ERbeta by immunohistochemistry in 353 stage II primary breast tumors from patients treated with two years adjuvant tamoxifen, and generated gene expression profiles for a representative subset of 88 tumors. Results: ERbeta was associated with increased survival (distant disease-free survival, P=0.01; overall survival, P=0.22), and in particular within ERalpha-negative patients (P=0.003; P=0.04), but not in the ERalpha-positive subgroup (P=0.49; P=0.88). Lack of ERbeta conferred early relapse (hazard ratio, 14; 95% CI, 1.8-106; P=0.01) within the ERalpha-negative subgroup even after adjustment for other markers. ERalpha was an independent marker only within the ERbeta-negative tumors (hazard ratio, 0.44; 95% CI, 0.21-0.89; P=0.02). An ERbeta gene expression profile was identified and was markedly different from the ERalpha signature. Conclusion: Expression of ERbeta is an independent marker for favorable prognosis after adjuvant tamoxifen treatment in ERalpha-negative breast cancer patients, and involves a gene expression program distinct from ERalpha. These results may be highly clinically significant, because in the U.S. alone, approximately 10,000 women are diagnosed annually with ERalpha-negative/ERbeta-positive breast carcinoma and may benefit from adjuvant tamoxifen. Keywords: Disease state analysis 88 breast cancer tumor samples were analyzed on 2-color cDNA microarrays containing ~27K reporters with Stratagene Universal Human Reference RNA as the common reference sample.