Wild-type oestrogen receptor beta (ERb1) mRNA and protein expression in Tamoxifen-treated post-menopausal breast cancers

This study has tested the hypothesis that comparison of protein and mRNA expression for ERalpha and ERbeta1 by human breast cancers provides novel information relating to the clinical and pathological characteristics of human breast cancers. Expression of ERalpha and ERbeta1 was identified in 167 invasive cancers from postmenopausal women treated only with endocrine therapy. The cohort included 143 cases receiving only adjuvant Tamoxifen following surgery. ERalpha and ERbeta1 expression was analysed by immunohistochemistry and reverse transcription RT-PCR and compared with clinical progression of individual cancers. ERalpha protein was closely associated with the corresponding RNA detected by RT-PCR (Chi-square, P<0.001). In contrast, ER beta 1 protein and mRNA were inconsistent. Although an association was identified between ER alpha and ER beta mRNAs (Chi-square, P <0.001) and between ERalpha protein and ERbeta1 mRNA (Chi-square, P<0.027), no association was identified for the ER alpha and ER beta 1 proteins detected by immunohistochemistry. ER beta 1 was not associated with outcome. However, in the absence of ER alpha, ER beta 1 protein expression was associated with elevated cell proliferation. There was a trend for the ER beta 1 protein-positive cases to have a worse outcome, both within the group as a whole as well as within the ER alpha-positive Tamoxifen-treated cases. This study has confirmed the hypothesis that expression of ER alpha is an important determinant of breast cancer progression, and has further demonstrated that ER beta 1 may play a role in the response of breast cancers to endocrine therapy.