Ultrastructural and Immunohistochemical Study of Salivary Duct Carcinoma of the Parotid Gland

A case of salivary duct carcinoma of the parotid gland found in an 81-year-old man was studied by light microscopy, immunohistochemistry, and electron microscopy. Histologically, the tumor was composed of elongated cords of cells and ductal structure with desmoplastic stromal reaction. Tumor cell nests sometimes showed central comedonecrosis. Immuno-histochemically, the tumor cells were positive for cytokeratin and epithelial membrane antigen, and they were negative for S-100 protein and muscle-specific actin. Electromicroscopi-cally, two cell types were identified. The first cell type showed electron-lucent cytoplasm with scant organelles. The second type cell contained numerous mitochondria. Neither acinar nor myoepithelial cell differentiation was observed. These findings suggest that salivary duct carcinoma originates from the interlobular or excretory ducts.