Diagnostic approach of primary salivary clear cell tumors: histopathological and immunohistochemical study

ABSTRACT

It is becoming increasingly evident that primary clear cell tumors [not variants of other known salivary tumors] represent a heterogeneous group of neoplasms. This group had been referred to clear cell carcinoma, clear cell epithelialmyoepithelial carcinoma and clear cell myoepithelial carcinoma. This work aims to study the histopathological criteria for diagnosis of primary salivary clear cell tumors and to investigate immunohistochemically their interrelationship with regard to myoepithelial differentiation 110 cases of salivary tumors were identified in the files at pathology department, Mansoura faculty of medicine through the period from 2000 to 2006. These cases were reviewed, and sixteen cases with clear cell features were rulled and evaluated further. Seven out of the sixteen cases were clear cell variants of oncocytoma, mucoepidermioid carcinoma, acinic cell carcinoma and were rulled out. The remaining nine cases could be classified as primary salivary clear cell tumors including 5 clear cell carcinomas, 3 epithelial-myoepithelial carcinomas, and 1 clear cell myoepithelial carcinoma. Histochemical [periodic acid-Schiff, with and without diastase treatment] and immunohistochemical studies were performed on formalin-fixed, paraffin-embedded sections using the labeled streptavidin-biotin-peroxidase complex to asses reactivity for S100, alpha smooth muscle actin, and broad spectrum cytokeratin. Six men and three women aged 30 to 62 years with mean age 46 yrs were participated in the study, and most presented with a painless mass. The parotid gland was the most common site [n = 7]. Clear cell carcinoma show positive staining for cytokeratin in all the studied cases [100%] and none of the cases show reactivity for smooth muscle actin confirming the epithelial origin of these tumors. Two out of five cases of CCC showed positive staining for S-100. Epithellal-myoepithelial carcinomas express S-100 and smooth muscle actin in the clear cell and the bimodal cell population with a ductal pattern was confirmed by cytokeratin cocktail immunohistochemistry thus confirming the myoepithelial nature of the tumors. Clear cell myoepithelial carcinoma show reactivity to cytokeratin, alpha smooth muscle actin and S-100. We concluded that there is no definitive immunohistochemical evidence of myoepithelial differentiation in clear cell carcinoma, indicating that it is probably morphogenetically distinct from epithelialmyoepithelial carcinomas and clear cell myoepithelial carcinoma, both tumors with diagnostically requisite myoepithelial differentiation