Estrogen receptor (ER) is the prototype therapy predictive marker in oncology. The ER is now known to exist in two main forms with similar overall structure: ER-alpha and ER-beta. Both forms may be expressed in breast cancer. The aim of this study was to examine breast cancer outcome in relation to expression of ER-beta. In this investigation, we measured the expression of ER-alpha protein and ER-beta mRNA in 121 extracts of invasive breast cancer. Association of expression with clinical outcome was examined using Kaplan-Meier and Cox regression analyses. While ER-alpha expression was associated with good patient outcome [hazard ratio (HR) for death from breast cancer 0.37; 95% confidence interval (CI) 0.17-0.84; p = 0.017], ER-beta predicted poor outcome (HR for death from breast cancer 2.49; 95% CI 1.10-5.63; p = 0.028). Based on these findings, we conclude that ER-beta may have a different biological role from that of ER-alpha in breast cancer.
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