Ultrastructure of the chondroid regions of benign mixed tumor of salivary gland

Abstract

Methods of light and electron microscopy were employed to determine the exact nature of the chondroid portions of the benign mixed tumor of salivary gland. Although these regions could not be distinguished from normal hyaline cartilage when examined with the light microscope, no normal or metaplastic chondrocytes could be identified when the ultrastructure of these regions was examined with the electron microscope. Instead, neoplastic myoepithelial cells embedded in a matrix quite similar to that of immature hyaline cartilage were found to be present. It is concluded that in the benign mixed tumor neoplastic myoepithelial cells undergo partial metaplasia enabling them to produce a typical chondroid matrix. Further, because of the similarity in structure and function between myoepithelial cells and visceral smooth muscle cells, it is suggested that the myoepithelial cell is of mesenchymal origin and, therefore, after metaplasia entirely capable of producing a mesenchymal mucin.

Epithelial-mesenchymal transdifferentiation and extracellular matrix gene expression in pleomorphic adenomas of the parotid salivary gland

“…13 In line with previous morphological observations 9,11,13,14,26 and in vitro studies, 27,28 our results establish a complete transition pathway from a pure epithelial to a mixed and finally a true mesenchymal cell phenotype within pleomorphic adenomas (Table II). Whereas cells in purely tubular areas showed only epithelial characteristics, many cells in tubulomyxoid areas had a mixed phenotype.…”

SOX‐10 expression in cutaneous myoepitheliomas and mixed tumors

“…The relationship between myoepithelial cells and mixed tumors has been heavily debated in the literature, in particular with regard to two issues: (i) whether myoepithelial cells are the source of the mesenchymal components of mixed tumors, and (ii) whether hyaline cells are of myoepithelial lineage. With respect to the first issue, many authorities have argued that the myoepithelial cell, with its physiologic capacity to elaborate components of connective tissue, is the cell responsible for producing the stroma of mixed tumors . This argument has largely rested on the fact that the outer layer of myoepithelial cells surrounding glandular tissue appears to form a morphologic continuum with detached myoepithelial cells and that these cells blend into the stromal elements; that, ultrastructurally, cells within the mesenchymal‐appearing areas contain actin myofilaments; and that these cells label with S100 and actin, which both label myoepithelial cells .…”

Myoepithelium of salivary glands

“…IN NEOPLASIA The variety of neoplasms arising from salivary glands is due in part to the extent to which MEC participate (Dardick and van Nostrand, 1987b). Few if any are found in the monomorphic adenomas (Chaudhry et al, 1983;Daley et al, 1984;Guccion and Redman, 1986;Luna and Mackay, 1976;Youngberg and Rao, 19791, they are present but not prominent in adenoic cystic carcinomas (Chaudhry et al, 1986;Eneroth et al, 1968;Tandler, 19711, and they are a major component of pleomorphic adenomas (Batsakis et al, 1983;Dardick and van Nostrand, 1985;Dardick et al, 1982;David and Buchner, 1982;Doyle et al, 1968;Eneroth and Wersall, 1966;Hamperl, 1970;Hubner et al, 1971;Mylius, 1960;Welsh and Meyer, 1968) and epithelialmyoepithelial carcinomas (Donath et al, 1972). Pleomorphic adenomas in which MEC are the principal cell types are called myoepitheliomas (Dardick et al, 1989).…”

“…The pleomorphic adenomas have generated a great deal of interest because they produce unusual mesenchymal patterns, such as chondroid and myxoid areas, into which spindle cells seem to stream from the neoplastic epithelium (Doyle et al, 1968). For many years there have been at least three different explanations for this phenomenon.…”