Undifferentiated carcinoma of the parotid gland. Case report with electron microscopic findings.

Two cases of undifferentiated carcinoma of the parotid gland were studied by light and electron microscopy. Light microscopy showed nests of ovoid cells with scanty cytoplasm and pyknotic nuclei in two cases. One case was the small-cell type, and another one was the large-cell type histopathologically. Electron microscopy showed two distinct cell types in each tumor: Case 1 (small-cell type). - An epithelial-like cell, and an irregular-shaped cell containing bundles of filaments suggesting myoepithelial differentiation. Case 2 (large-cell type). - An epithelial-like cell, and a large cell containing secretory-like granules. These findings support a salivary duct epithelial origin for these tumors.