Ultrastructural and immunohistochemical study of small cell neuroendocrine carcinoma of the parotid gland.

A case of small cell neuroendocrine carcinoma of the parotid gland is presented with immunohistochemical and electron microscopic studies. Small cell neuroendocrine carcinoma is extremely rare and is often difficult to distinguish from malignant lymphoma, adenoid cystic carcinoma, and undifferentiated carcinoma. Under light microscopy, the tumor cells consisted of solid sheets and nests of small tumor cells. Immunohistochemically, they were positive for KL-1 and EMA, and focally positive for NSE and synaptophysin. Observation using an electron microscope showed membrane-bound neuroendocrine granules in some tumor cells. Histological evaluation indicated that the present case was small cell carcinoma of the parotid gland, showing a neuroendocrine variety.