Estrogen receptor α and β profiling in human breast cancer

Background. The identification of a second estrogen receptor (ER-β) has significant implications for therapeutic strategy in breast cancer management arising from the potential agonist effect of Tamoxifen at estrogen receptor sites and as such, antiestrogen therapy may be inappropriate in patients with a dominance of ER-β. Methods. To determine the proportion of breast cancer patients who may be so at risk, we developed a novel multiplexed RT-PCR technique to establish the relative ER-α and ER-β levels in 53 primary breast cancers, 11 normal breast tissues and six cell lines. We further assessed the prognostic significance of receptor status relative to the Nottingham prognostic index (NPI). The ER-α and ER-β status was also determined by immunohistochemistry using previously published and ‘in-house’ scoring systems. Results. Using RT-PCR analysis, 46 tumours were hormone receptor positive (ER+) with 42 displaying ER-α predominance. Comparison with immunohistochemistry demonstrated 44/53 (ER-α) and 27/50 (ER-β) concordance rates. There was no significant difference in the NPI between ER-α and ER-β predominant cohorts or between ER+ and ER− cohorts. Conclusion. This study identifies the existence of a subgroup of ER+ patients in whom Tamoxifen therapy may be inappropriate and has significant implications for adjuvant therapy of primary breast cancer.