The myoepithelium in human breast fibroadenoma

Tubular adenoma of the breast: an immunohistochemical study of ten cases

Ten cases of so-called "tubular" adenoma and six cases of fibroadenoma of the breast have been investigated with an immunohistochemical technique with the aim of providing both more details on their immunophenotype and of ascertaining the possible relationships between tubular adenoma and fibroadenoma. Smooth Muscle Actin, Cytokeratin 14, GFAP, S-100 Protein and Vimentin immunoreactivity have clearly demonstrated that cells with myoepithelial immunophenotype are one of the major cell components in breast adenomas. Epithelial Membrane Antigen (EMA), Human Milk Fat Globule II (HMFG II), Estrogen and Progesterone receptors have been detected in adluminal epithelial cells exclusively. Furthermore, Smooth Muscle Actin and Vimentin highlighted an abundant myofibroblastic component, intermingled with tubular structures in both tumor types. A low percentage (10-22%) of adluminal cells and of myofibroblasts showed Ki-67 immunoreactivity in tubular adenomas and in fibroadenomas, whereas only rare myoepithelial cells demonstrated Ki-67 positivity in both tumor types. These data seem to indicate that several cell components of both epithelial and mesenchymal origin (epithelial cells, myoepithelial cells, myofibroblasts) are involved in the genesis of tubular adenomas. The morphological and immunohistochemical features of tubular adenomas closely resemble, in some areas of the tumors, those of fibroadenoma. Therefore, they may represent histogenetically related neoplasms with exuberant ductular component in tubular adenomas and predominant stromal component in fibroadenoma.

Intralobular growth of myoepithelial cell carcinoma of the breast

Two cases of intralobular carcinoma of the breast showing myoepithelial cell differentiation are reported. One was an in situ lesion localized within a fibroadenoma; the second was predominantly in situ, but areas of invasion were present. The neoplastic cells had round to ovoid nuclei and were polygonal to spindle in shape displaying glycogen rich clear cytoplasm. Alpha-smooth muscle actin was present in the cytoplasm of the neoplastic cells in both cases. In one case the same cells displayed cytoplasmic microfilaments at electron microscopic level. Intralobular growth of neoplastic myoepithelial cells has never been described in the literature, and this line of differentiation has to be added to the endocrine and apocrine features occasionally observed in in situ lobular carcinomas of the breast.

The expression of intermediate filaments in canine mammary glands and their tumors

Monoclonal antibodies specific for different types of intermediate filaments (cytokeratin, vimentin, desmin and neurofilaments) were used to study the histogenesis of canine mammary glands and 57 canine mammary tumors by immunocytochemistry. The intra- and interlobular duct epithelium, acinar, and intralobular myoepithelial cells stained positively for cytokeratin. Peripheral ductal and acinar cells, as well as interstitial cells, stained positively for vimentin. A similar staining pattern was seen in adenomas, complex adenomas, benign mixed tumors, ductular carcinomas, and one myoepithelioma-like tumor. Additionally, cytokeratin positive cells were scattered interstitially in one single adenoma, most complex adenomas, some benign mixed tumors, complex carcinomas, and in the malignant mixed tumors. All stromal cells stained positively for vimentin. The fibrosarcomas were positive only for vimentin, while the following expressed both desmin and cytokeratin: epithelial-like cells in one adenoma, three complex adenomas, the myoepithelioma-like tumor, the single comedo carcinoma, two complex carcinomas, the single lobular carcinoma, one malignant mixed tumor, and three osteosarcomas. Epithelial-like cells in one adenoma, six complex adenomas, two benign mixed tumors, two complex carcinomas, the lobular carcinoma, and the malignant schwannoma stained for neurofilaments. Three tumors, one adenoma, one complex adenoma, and the lobular carcinoma expressed both desmin and neurofilaments in addition to cytokeratin and vimentin. The results show the expression of different types of intermediate filaments and indicate that there might be a stem cell origin in most of the canine mammary tumors.

A monoclonal antibody CIBr17 recognizes a myoepithelium-specific antigen in human mammary gland

A murine monoclonal antibody (MAb) CIBr17, raised against the human breast carcinoma cell line PMC42, reacts specifically with myoepithelial cells in normal human breast. This IgGl antibody recognizes a approximately 110kDa glycoprotein that is expressed on the cell surface and junctional membranes of PMC42 monolayer cultures. The CIBr17 antigen is present in two major glycosylated forms with approximate pls of 5.2 and 5.5 respectively in PMC42 cells. The tissue specificity of CIBr17 was assessed on frozen sections of PLP-fixed tissues by means of a 4-layer immunoperoxidase technique. CIBr17 has reacted with a variety of epithelium-derived tissues and some smooth muscle cells. Within many epithelial tissues, CIBr17 has demonstrated specific staining of particular epithelial cell types. Within normal breast and most benign breast lesions, antibody CIBr17 stained only myoepithelial cells. No staining of luminal epithelium, basement membranes or stromal elements was observed. In sclerosing adenosis, CIBr17 stained areas of pronounced myoepithelial differentiation, while in duct epitheliosis variable staining of proliferating cells was observed. In breast carcinomas, CIBr17 demonstrated variable antigen expression. In most tumors, CIBr17 either did not stain any tumor cells or stained only a small number of tumor cells spread randomly throughout the tumor. In several ductal carcinomas, however, CIBr17 stained the majority of tumor cells.

Pseudoangiomatous hyperplasia of mammary stroma

Grossly circumscribed, nonhemorrhagic breast masses consisting of mammary stromal proliferations that simulated vascular lesions were studied in nine women. Histologically, a striking pattern, which appeared to consist of complex inter-anastomosing channels lined by slender spindle cells, was present in the mammary parenchyma. The importance of this benign lesion, referred to as pseudoangiomatous hyperplasia of mammary stroma, is its distinction from angiosarcoma. The patients ranged in age from 22 to 52 years; all were premenopausal. Each presented with a palpable unilateral mass, measuring up to 7 cm in diameter. The patients were treated by excisional biopsy and remained well for up to 2.5 years after excision. One patient had two local recurrences within one year of the original excision, and a second patient had a local recurrence at 14 months. No patient had another concurrent or metachronous malignant tumor of the breast or other organ, and no abnormal hormonal status was found. Complete local excision appears to be adequate treatment. It remains to be determined whether this is a neoplastic process. However, there is no evidence that it is a precursor of angiosarcoma, and ultrastructural observations demonstrate that the spaces found in the lesion are not true vascular channels. Rather, they appear to arise by a process that involves disruption and separation of stromal collagen fibers. Since small foci of this change are common in hyperplastic breast tissue from premenopausal women, it is likely that the development of a discrete tumor with this pattern represents an exaggerated form of stromal hyperplasia.

Intermediate-sized filaments of the prekeratin type in myoepithelial cells

Myoepithelial cells from mammary glands, the modified sweat glands of bovine muzzle, and salivary glands have been studied by electron microscopy and by immunofluorescence microscopy in frozen sections in an attempt to further characterize the type of intermediate-sized filaments present in these cells. Electron microscopy has shown that all myoepithelial cells contain extensive meshworks of intermediate-sized (7--11-nm) filaments, many of which are anchored at typical desmosomes or hemidesmosomes. The intermediate-sized filaments are also intimately associated with masses of contractile elements, identified as bundles of typical 5--6-nm microfilaments and with characteristically spaced dense bodies. This organization resembles that described for various smooth muscle cells. In immunofluorescence microscopy, using antibodies specific for the various classes of intermediate-sized filaments, the myoepithelial cells are strongly decorated by antibodies to prekeratin. They are not specifically stained by antibodies to vimentin, which stain mesenchymal cells, nor by antibodies to chick gizzard desmin, which decorate fibrils in smooth muscle Z bands and intercalated disks in skeletal and cardiac muscle of mammals. Myoepithelial cells are also strongly stained by antibodies to actin. The observations show (a) that the epithelial character, as indicated by the presence of intermediate-sized filaments of the prekeratin type, is maintained in the differentiated contractile myoepithelial cell, and (b) that desmin and desmin-containing filaments are not generally associated with musclelike cell specialization for contraction but are specific to myogenic differentiation. The data also suggest that in myoepithelial cells prekeratin filaments are arranged--and might function--in a manner similar to the desmin filaments in smooth muscle cells.