Expression of wild-type estrogen receptor β protein in human breast cancer: Specific correlation with HER2/neu overexpression

Expression of estrogen receptor β (ERβ) protein in human breast cancer and correlation with clinicopathological factors have been reported by many investigators, but many of them used ERβ antibodies that react with both wild‐type ERβ (ERβwt) and splicing variant isoform. Therefore, the frequency and correlation with clinicopathological factors of ERβwt expression remain to be established. In the present study a monoclonal antibody EMR02, specific for ERβwt, was used in formalin‐fixed paraffin‐embedded sections from 225 female primary breast cancer patients diagnosed as having invasive ductal carcinoma. Expression of ERα, progesterone receptor (PgR) and HER2/neu were also investigated by immunohistochemistry. For ERβwt, ERα and PgR, positivity was defined as nuclear staining in >10% of the cancer cells. HER2/neu overexpression was defined as a Hercep test score 3+. Positivity for ERβwt, ERα, PgR and HER2/neu overexpression was 55%, 74%, 61% and 25%, respectively. The expression of ERβwt had a positive correlation with ERα (P = 0.018) and PgR (P = 0.02). There was significant positive correlation between ERβwt expression and HER2/neu overexpression (P