Distinct expression patterns of ER and ER in normal human mammary gland

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Abstract
Two oestrogen receptors (ERs) have been identified to date-the "classic" ER alpha and the more recently described ER beta. Although much is known about ER alpha at the mRNA and protein levels, our knowledge of the expression and distribution of ER beta protein is much more limited. The aim of this study was to compare the cellular distribution of ER alpha and ER beta in normal human mammary gland. Formalin fixed, paraffin wax embedded material was obtained from reduction mammoplasty specimens, normal tissue adjacent to breast tumour, or fibroadenoma. Sections were immunohistochemically stained for ER alpha, ER beta, and the progesterone receptor. The staining pattern for each antibody was evaluated and compared. ER alpha was restricted to the cell nuclei of epithelial cells lining ducts and lobules. Although ER beta was also seen in these cells, additional strong staining was detected specifically in the cell nuclei of myoepithelial cells. Occasional staining was seen in surrounding stromal and endothelial cell nuclei and in lymphocytes. ER subtypes have distinct distribution patterns in the normal mammary gland. The widespread distribution of ER beta suggests that it may be the dominant ER in the mammary gland where it may be acting as a natural suppressor.