Oncocytic carcinoma in the submandibular gland: report of a case based on anti-mitochondrial immunohistochemical observations.

Oncocytic carcinoma arising in the submandibular gland is a very rare tumor that has only previously been reported in nine cases. This paper describes an additional case of oncocytic carcinoma in the right submandibular gland. The patient was a 55-year-old Japanese male who was presented with a 3 cm right submandibular mass. Both radical resection of the tumor and right supraomohyoid neck dissection were performed. Histologically, the tumor cells exhibited an abundant eosinophilic cytoplasm, which appeared to be finely granular, and invaded the surrounding tissues. In addition, perineural invasion was also observed. Electron microscopy demonstrated the presence of an abundance mitochondria in the cytoplasm of the tumor cells. However, since the fine structure of cytoplasm was destroyed by fixation and embedding of the tissue for the light microscopy, the cytoplasm of the tumor could not be observed clearly. Immunohistochemically, anti-mitochondrial antibody positivity was evident in the cytoplasm of the tumor cells. Consequently, we diagnosed the mass as oncocytic carcinoma. Usually, electron microscopy is necessary to diagnose oncocytic lesions, but the paraffin-embedded tissue was not suitable for electron microscopy. Immunohistochemistry using an anti-mitochondrial antibody was found to be useful and helpful for the diagnosis of oncocytic lesions.