AIM: Two oestrogen receptors (ERs) have been identified to date—the “classic” ERa and the more
recently described ERb. Although much is known about ERa at the mRNA and protein levels, our
knowledge of the expression and distribution of ERb protein is much more limited. The aim of this study
was to compare the cellular distribution of ERa and ERb in normal human mammary gland.
METHODS: 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 ERa, ERb, and the progesterone receptor. The staining pattern for
each antibody was evaluated and compared.
RESULTS: ERa was restricted to the cell nuclei of epithelial cells lining ducts and lobules. Although ERb
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.
CONCLUSIONS: ER subtypes have distinct distribution patterns in the normal mammary gland. The widespread
distribution of ERb suggests that it may be the dominant ER in the mammary gland where it may
be acting as a natural suppressor
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