Estrogen receptor-β:: Role in breast cancer

The estrogen receptor (ER) assay is widely used to select sensitivity to hormone therapy in patients with breast cancer. Recently, a new form of ER, known as ERbeta was identified, the classic form now being denoted ERalpha. In this investigation, ERalpha and ERbeta were measured at the mRNA level in 181 primary breast cancers and 33 fibroadenomas. We found that ERbeta was expressed less frequently in the carcinomas compared to the fibroadenomas (P = 0.007). In the carcinomas, ERbeta was expressed less frequently than ERalpha mRNA (P = 0.001). In the carcinomas, ERalpha mRNA was positively related to both ER and progesterone receptor (PR) protein levels. In contrast, ERbeta showed an inverse relationship with both ER and PR protein levels. These findings suggest that this widely used ER protein assay is mostly measuring ERalpha and is unlikely to be detecting ERbeta. Further patient follow-up is necessary to show whether ERbeta has any predictive or prognostic value in breast cancer.