Oncocytic carcinoma of the parotid gland - A case report

BACKGROUND: Oncocytic carcinoma is a rare malignant tumor of the salivary gland. Abundant, granular, eosinophilic cytoplasm is recognized as an oncocytic feature that reflects an accumulation of mitochondria. Ultrastructural study or immunohistochemical staining using antimitochondrial antibody can confirm the oncocytic nature of the tumor. However, there have been no data on whether immunocytochemical staining for human mitochondria aids in the confirmation of the oncocytic nature of oncocytic carcinoma. CASE: A 61-year-old man presented with a swelling in the left lower cheek. Computed tomography demonstrated a solid, isodense tumor in the parotid gland. An excisional biopsy of the tumor was performed, and an enlarged regional lymph node was removed. Imprint cytology of the lymph node showed cohesive cell clusters with lymphocytes. The clusters were composed of tumor cells that had characteristic abundant, granular cytoplasm and round to oval, centrally or eccentrically located nuclei with increased, fine chromatin and distinct nucleoli. Immunocytochemical staining revealed granular immunoreactivity of the cytoplasm for human mitochondria. Histology demonstrated tumor invasion in the normal gland and adjacent skeletal muscles. All tumor cells showed positive cytoplasm with antimitochondrial antibody by immunohistochemistry. Ultrastructural studies demonstrated packed mitochondria in the cytoplasm of the tumor. CONCLUSION: Immunocytochemical staining for human mitochondria help confirm the oncocytic nature of oncocytic carcinoma in cytologic specimens.