Low-grade mucoepidermoid carcinoma of salivary glands: characteristic immunohistochemical profile and evidence of striated duct differentiation

Abstract

The purpose of the present study is to determine the presence and distribution of epithelial and myoepithelial cells in mucoepidermoid carcinoma (MEC) of salivary glands and to compare them with normal salivary gland tissue and other primary carcinomas. This is in order to establish novel diagnostic criteria and to better understand MEC histogenesis. Formalin-fixed paraffin-embedded tissues from ten well-differentiated MECs, three adenoid cystic carcinomas (ACC), four acinic cell carcinomas (AC), and three epithelial-myoepithelial carcinomas (EMCC) of salivary glands were studied with immunohistochemistry using antibodies that recognise antigens indicative of epithelial and myoepithelial cell differentiation. An anti-mitochondrial antibody was also employed. Normal salivary tissue was present for comparative study in non-tumorous areas of the same section from 12 cases. MEC contained numerous keratin-positive cells. Anti mitochondrial antibody was diffusely positive in all ten of these tumours. Smooth muscle actin, h-caldesmon, and smooth muscle heavy chain myosin, which are indicative of myoepithelial cell differentiation, were negative. Rare cells in only one case were stained by calponin. Cytokeratin 14 (CK14) and anti mitochondrial antibody stained cells located mainly at the periphery of neoplastic nests and cystic spaces, while CK7 was mainly present in cells bordering gland lumina (zoning pattern). The immunohistochemical cell profile was similar to that seen in striated normal ducts. All others tumours studied showed a different immunohistochemical pattern, mostly consisting of a lack of mitochondrion-rich cells and the presence of myoepithelial cells in ACC and EMCC. Immunoreactivity in MEC for CK7, CK14 and mitochondrial antibodies appears as a peculiar pattern of staining, different from that of other salivary gland tumors; this seems helpful for diagnostic purposes. In addition, a differentiation of the "striated duct phenotype" is suggested.

Immunohistochemical expression of cytokeratins 7 and 20 in malignant salivary gland tumors

“…In general, CK7 was reported to be expressed by the vast majority of studied salivary gland tumors, including benign and malignant tumors. 19,[22][23][24][26][27][28][29][30][31] These results are in accordance with our findings showing that all cases of malignant salivary gland tumors were positive for CK7, despite differences in intensity, positivity, and distribution of staining. Regarding the latter, the preferential CK7 immunohistochemical expression in certain subtypes of tumor cells observed in our study, such as luminal over myoepithelial cells in adenoid cystic carcinomas, agrees with the findings of other authors and partially reiterates the distribution of CK7 expression in the different cellular compartments of normal salivary glands.…”

“…Although several investigators have examined the expression of CKs in neoplastic lesions of salivary glands, 19,[21][22][23][24][25][26][27][28][29][30][31] to the best of our knowledge this is the first time that the combined CK7 and CK20 profile of malignant salivary gland tumors is analyzed in a sizeable group of these tumors.…”

“…Such studies have shown that different CKs are localized in the various compartments of normal salivary glands, for example, CK8 and CK18 are expressed in the luminal duct and acinar cells, while CK5 and CK14 are primarily seen in basal duct cells and myoepithelial cells. [21][22][23][24] Interestingly, CK7 has been shown to be expressed to a different degree in the various epithelial salivary gland elements; more specifically, the luminal cells of the salivary ducts are strongly positive for CK7, while the acinar, basal, and myoepithelial cells stain with less intensity or, according to some investigators, not at all. [21][22][23][24] On the other hand, CK20 has been reported to be consistently absent from all salivary gland epithelial elements.…”

“…[21][22][23][24] Interestingly, CK7 has been shown to be expressed to a different degree in the various epithelial salivary gland elements; more specifically, the luminal cells of the salivary ducts are strongly positive for CK7, while the acinar, basal, and myoepithelial cells stain with less intensity or, according to some investigators, not at all. [21][22][23][24] On the other hand, CK20 has been reported to be consistently absent from all salivary gland epithelial elements. 22,24,25 The pattern of CK expression in normal salivary glands has been demonstrated to be recapitulated to some extent in their benign and malignant neoplasms.…”

“…[21][22][23][24] On the other hand, CK20 has been reported to be consistently absent from all salivary gland epithelial elements. 22,24,25 The pattern of CK expression in normal salivary glands has been demonstrated to be recapitulated to some extent in their benign and malignant neoplasms. Nonetheless, differences among tumors of different histopathologic type, different tumors of the same type, or even different areas of the same tumor were evident.…”