MIOEPITHELIAL CELLS: STRUCTURE, FUNCTION, AND THEIR ROLE IN NORMAL AND NEOPLASTIC TRANSFORMATION OF THE BREAST
Authors: Adamovych Оlena , Chelpanova Ilona , Paltov Yevgeniy , Sohuyko Rostyslav , Poliiants Artur , Sopneva Nadia 
Published: October 2023

Abstract. Myoepithelial cells (MECs) are characteristic of exocrine glands and are responsible for synthesizing the extracellular matrix, particularly the structural components of the basal membrane. MECs are of epithelial origin and exhibit contractile function, which aids in milk ejection from the ducts during lactation. Scientiﬁc literature suggests that MECs act as suppressors of tumors and play an important diagnostic role in mammary gland pathology, especially in distinguishing diﬀ erent neoplastic processes.Research objective: T o elucidate the histological features and immunohistochemical veriﬁ cation of myoepithelial cells in normal breast tissue and their role in neoplastic transformation of the mammary gland.Materials and Methods. The histological examination of myoepithelial cells of the mammary gland was conducted on archival slides from the Department of Histology, Cytology, and Embryology, Danylo Halytsky Lviv National Medical University. Histological sections, stained with hematoxylin and eosin, as well as immunohistochemical markers p63 (Clone 4A4, Masterdiagnostica) and cytokeratin 5/6Ab-2 (D5/16 B4, Thermoscientiﬁ c) for conﬁ rming the myoepithelial origin of the cells, were analyzed under a light microscope (UlabXSP-137TLED) with 10x and 40x objectives and a 10x eyepiece. Photographs were taken using an XCAM 1080P camera.Research Results. The structural units of the mammary gland (MG) are ductal-l obular formations, the terminal portions of which have an alveolar shape and are formed by secretory exocrine cells with underlying myoepithelial cells – basket-like cells. Identiﬁ cation of myoepithelial cells using conventional histological staining techniques such as hematoxylin and eosin does not always provide a clear understanding of their topography. All myoepithelial cells are located on the basal membrane and contribute to the synthesis of its components (laminin, entactin, etc.). The myoepithelial cell layer, which is consistently present in the normal mammary gland, can appear diﬀ erently: resembling smooth muscle or epithelioid cells, having a stellate or spindle- shaped form, or not being visualized at all. It has been shown that p63 is a sensitive and speciﬁ c nuclear myoepithelial marker, expressed in myoepithelial cells of the normal mammary gland, in residual lobular acini, sclerosing adenosis, carcinoma in situ, and not detected in invasive carcinomas. It can be included in immunohistochemical panels aimed at identifying myoepithelial cells in diagnostically challenging breast pathologies.Conclusions. Myoepithelial cells in the mammary glands play a key role in their function, facilitating the process of milk secretion. However, in certain cases, they also play an important role in the development of neoplastic transformations. Intercellular connections between secretory and myoepithelial cells indicate that the last ones suppress both the progression of carcinoma in situ to invasive breast cancer and the carcinomainduced angiogenesis. The use of the immunohistochemical marker p63 is mandatory in the panel of antibodies to identify myoepithelial cells in the mammary gland and diﬀ erentiate between benign and malignant lesions.