The Pattern of Expression of Human Placental Lactogen Across Normal, Lactational, and Malignant Mammary Epithelium

The immunoexpression of human placental lactogen (hPL) in mammary epithelium is not well studied in the literature. Our overall objective was to delineate the distribution pattern of hPL across mammary epithelia of varying levels of differentiation. This is the first research to study the level of expression of hPL in human lactational change epithelium. Immunohistochemistry (IHC) for hPL was performed on archival formalin-fixed paraffin-embedded tissue blocks of 97 cases. These consisted of 53 invasive ductal carcinomas, 21 lactational change cases, and 23 cases of normal mammary tissue. The results of this study show underexpression of hPL in malignant epithelium compared to normal and lactational groups individually and combined as a non-malignant group. However, a higher expression of hPL was noted in mammary carcinoma of axillary lymph node (ALN)-positive patients compared to ALN-negative cases. There was no statistically significant difference between hPL expression and tumor grade, estrogen receptors (ER), progesterone receptors (PR), or human epidermal growth factor receptor 2 (HER2) status. The comparison of the immunoexpression of hPL in malignant epithelium versus lactational change epithelium may provide the basis for future studies on the possible role of hPL in the protective mechanism of lactation tissue from carcinogenesis. Our results could be explained by the proposed mechanism in the literature, which is that breast cancer cells have a potential inhibitory effect on the translation of human chorionic somatotropin hormone (CSH) mRNA into hPL protein. Our results support the literature findings of a poorer prognostic outcome for breast malignancies when hPL is expressed but require further studies using a more comprehensive range of clinical parameters.