An immunocytochemical method for fixed and paraffin-embedded human breast biopsies is reported for the detection of myoepithelial and epithelial cells using antibodies to myosin and keratin, respectively, and of basement membranes using antibodies to laminin and type IV collagen. Using these markers, myoepithelial cells can be clearly distinguished in the normal breast and in the benign breast diseases sclerosing adenosis, epitheliosis, and fibroadenoma. In sclerosing adenosis, myoepithelial cells form a major cellular component. A stromally derived spindle cell is identified which stains with myosin but not with keratin antibodies (myofibroblast). These cells are seen in one-fifth of the fibroadenomas. Although cells staining with myosin antibodies are seen in the infiltrating component of all 18 carcinomas examined, elongated cells staining with both myosin and keratin antibodies (myoepithelial-like) are seen in only one infiltrating carcinoma where they are interposed at the stromal-epithelial junction of the infiltrating tumor cells. In contrast to the situation in benign breast diseases, mature myoepithelial cells form a very minor component of the majority of infiltrating ductal carcinomas. Basement membrane proteins, laminin, and type IV collagen are present in normal breast, benign breast disease, and grade I infiltrating ductal carcinomas but are absent in carcinomas of grades II and III.

https://cancerres.aacrjournals.org/content/canres/42/11/4763.full.pdf

Distribution of Myoepithelial Cells and Basement Membrane Proteins in the Normal Breast and in Benign and Malignant Breast Diseases

A series of 23 primary invasive and 7 metastatic carcinomas was examined by light microscopy (LM), transmission electron microscopy (TEM) and immunofluorescence (IF), the latter employing an anti-actin antibody. The results were correlated with macroscopic features such as retraction and consistency. Stromal cells rich in actin, readily identified by IF in firm and retracted carcinomas, were rare or absent in neoplasms lacking these features. TEM established the myofibroblastic nature of these stromal cells. Alternate sections (LM, IF) of each neoplasm demonstrated that myofibroblasts were more numerous in “young” mesenchymal stroma than in densely sclerotic areas. The connective tissue adjacent to intraductal mammary carcinoma lacked myofibroblasts, suggesting that epithelial stromal invasion is required to evoke a myofibroblastic stromal response. Myofibroblasts which possess synthetic (type III collagen) and contractile properties may well contribute to the firm consistency and retraction which characterize many carcinomas. The induction of myofibroblasts might represent an important host stromal response directed toward containment of invasive and/or metastatic carcinoma. This response may be especially important in neoplasms with weak antigenicity and/or slow doubling times.

Stromal myofibroblasts in primary invasive and metastatic carcinomas. A combined immunological, light and electron microscopic study.

Movements of the stiff sensory hairs, the stereocilia, which extend outwards from the apical surface of the hair cells in the auditory organ, are thought to have a key role in the process of transduction of sound energy into electrical impulses. Each stereocilium is supported by a paracrystalline axial bundle of actin filaments, which have identical polarities and are extensively cross-linked1–4. Recent immunohistochemical observations on whole mounts of the guinea pig organ of Corti indicated myosin-like immunoreactivity in association with hair cell stereocilia5. Considering the steric situation, it is, however, difficult to imagine any functional interaction between the bundled actin filaments and the assumed myosin molecules. Here we report that in semi-thin, transverse sections of quick-frozen, freeze-dried and plastic-embedded guinea pig organ of Corti, myosin-like immunostaining was restricted to the apical cytoplasm of hair cells and was not detected along the stereocilia. With respect to the immunohistochemical distribution of actin, myosin and the muscular Z-line protein, α-actinin, the apex of hair cells strongly resembles the intestinal epithelial brush border6–7.

Absence of myosin-like immunoreactivity in stereocilia of cochlear hair cells.

Evidence based on immunocytochemical staining and ultrastructure suggests that morphological gradations between epithelial and myoepithelial cells, and possibly between epithelial cells and alveolar-like cells occur in terminal ductal structures of rat and human mammary glands. The benign carcinogen-induced rat and benign human mammary tumors can contain epithelial, myoepithelial-like and alveolar-like cells, whereas the malignant counterparts mainly contain only epithelial-like cells. Clonal epithelial cell lines from normal rat mammary glands, benign tumors, and SV40-transformed human mammary glands can differentiate to either myoepithelial-like or alveolar-like cells. In those of the rat, the differentiation processes occur in steps: intermediate cells along the myoepithelial-like pathway resemble intermediates in terminal ductal structures in vivo, and can also generate certain well-differentiated mesenchymal elements of the original tumours. Differentiation of the benign rat cells to alveolar-like cells with mammatrophic hormones and retinoids in vitro leads to a reduction in their tumor-forming ability in vivo. Cell lines from malignant rat mammary tumors of increasing metastatic potential and from human ductal carcinomas largely fail to yield myoepithelial-like or alveolar-like cells and are relatively slow-growing. Growth of the rat mammary epithelial cells in culture is stimulated by a pituitary-derived mammatrophic growth factor (PMGF), prostaglandin E2, and α-transforming growth factor; the response of the malignant cell lines to PMGF is reduced. It is suggested that stem cells exist in the rat and human glands that are capable of differentiating to the other major cell types of the mammary parenchyma, and that during the carcinogenic process they generate genetically unstable cells which lose their ability to differentiate and attempt to maximise their intrinsically slow growth rate.

Stem cells and the development of mammary cancers in experimental rats and in humans

The distribution of the myoepithelial cells in 32 cases of ductal carcinoma-in-situ (DCIS) of the breast (11 not associated, 21 associated with invasive carcinoma) was investigated with a recently developed immunoperoxidase method for actin. Actin-rich myoepithelial cells were detected at the periphery of some ducts, however, their presence was neither constant nor continuous. Large areas of DCIS were devoid of a myoepithelial cell layer and the neoplastic cells were directly in contact with the stroma. No differences related to the histological pattern of DCIS or the presence and absence of invasive carcinoma were noted. The behaviour of the myoepithelial cells in ductal carcinoma appears different from that observed in cases of lobular carcinoma (Bussolati 1980) and of cystic disease, and may thus be of diagnostic interest. The selective destruction of myoepithelial cells in cases of DCIS might result in a focal disruption of the basement membrane, thus facilitating invasion.

Macartney Jc

Papers

Identification of myosin in human epithelial cancers with immunofluorescence.