Malignant oncocytoma of the parotid gland. A light and electron microscopic study.

A case malignant oncocytoma of the parotid gland occurring in a 91-year-old man is reported. The tumor recurred 10-months and 2 1/2 years after the primary excision. Both primary and recurrent tumors exhibited an infiltrative pattern. The histologic appearance of the original tumor and the recurrent lesion were similar, but there were areas of increased mitotic activity and pleomorphism in the latter. Ultrastructural examination of the recurrent tumor revealed that the cytoplasm was packed with mitochondria. The fine structure was, for the most part, similar to the benign variant reported previously. In the present tumor, however, intercellular spaces were more prominent and a basal lamina was not observed. The malignant oncocytoma occurs both in major and minor salivary glands. The tumor mostly affects the older age group, but the biologic behavior cannot be evaluated fully because of the paucity of cases reported and the lack of follow-up information.