Cellular expression of growth hormone and prolactin receptors in human breast disorders

Growth hormone (GH) and prolactin (PRL) exert their regulatory functions in the mammary gland by acting on specific receptors. Using isotopic in situ hybridization and immunohistochemistry, we have localized the expression of hGH receptor (hGHR) and hPRL receptor (hPRLR) in a panel of human breast disorders. Surgical specimens from adult females included normal breast, inflammatory lesions (mastitis) benign proliferative breast disease (fibroadenoma, papilloma, adenosis, epitheliosis), intraductal carcinoma or lobular carcinoma in situ, and invasive ductal, lobular or medullary carcinoma. Cases of male breast enlargement (gynecomastia) were also studied. In situ hybridization analysis demonstrated the co-expression of hGHR and hPRLR mRNA in all samples tested. Epithelial cells of both normal and tumor tissues were labelled. Quantitative estimation of receptor mRNA levels was regionally measured in areas corresponding to tumor cells and adipose cells from the same section. It demonstrated large individual variation and no correlation emerged according to the histological type of lesion. Receptor immunoreactivity was detected both in the cytoplasm and nuclei or in the cytoplasm alone. Scattered stromal cells were found positive in some cases, but the labeling intensity was always weaker than for neoplastic epithelial cells. Our results demonstrate the expression of the hGHR and hPRLR genes and their translation in epithelial cells of normal, proliferative and neoplastic lesions of the breast. They also demonstrate that stromal components express GHR and PRLR genes. Thus the putative role of hGH or hPRL in the progression of proliferative mammary disorders is not due to grossly altered levels of receptor expression.