Altered expression of epidermal growth factor receptor in non-involved tissue of cancer-containing breasts

Previous studies have identified functional differences in non-involved breast tissue from cancer-containing breasts. This study has examined the expression of epidermal growth factor (EGFR) protein and mRNA in the non-involved breast of over 100 cancer-containing breasts and compared these with the same number of normal breast tissues from age-matched women with no history of breast cancer. Immunohistochemistry with EGFR1 antibody applied to frozen sections was used for the detection of protein, and in-situ hybridization using a digoxigenin-labelled oligonucleotide probe was the method for detecting mRNA. EGFR protein was detected in myoepithelial cells and to a lesser extent in epithelial cells, where it was predominantly basal or baso-lateral. There was a significant difference in the extent of staining in ducts and lobules between non-involved tissue from cancer-containing breasts and age-matched normal breasts, it being significantly greater in the latter (P<0.001). Labelling for EGFR mRNA was greater and more consistent in myoepithelial cells than epithelial cells overall. Differences were found for intensity of labeling, with it being significantly greater for normal breast tissue (P<0.001) than non-involved tissue from cancer-containing breasts. There is reduced EGFR expression in normal breast tissue from cancer-containing breasts when compared to age-matched breast tissue from women with no history of breast cancer. The mechanisms underlying this are unclear but in previous studies we have identified alterations in myoepithelial cells in cancer-containing breasts and the present findings may represent altered myoepithelial cell function.