Oncocytic carcinoma

Definition Oncocytic carcinoma is a proliferation of cytomorphologically malignant oncocytes and adenocarcinomatous architectural phenotypes, including infiltrative qualities. These may arise de novo, but are usually seen in association with a pre-existing oncocytoma {1833}. Rarely, a benign appearing oncocytic tumour metastasizes following local recurrence {2498} and is designated carcinoma, despite the absence of malignant cellular morphology.

ICD-O code 8290/3

Epidemiology Men are affected in two-thirds of cases. A wide age range from 25-91 years has been reported with a mean age of 62.5 years {71}. This neoplasm represents only 5% of oncocytic salivary gland tumours and less than 1% of all salivary gland tumours {922}.

Localization Nearly 80% involve the parotid gland, 8% the submandibular gland, with all others in minor salivary glands.

Clinical features Typically there is a painless, nondescript mass in the parotid or submandibular gland. In cases of malignant transformation of a benign oncocytoma a rapid increase in size is noted after a period of slow growth. Facial nerve involvement may cause pain, paresis or neuropathy {922}.

Macroscopy They are firm, unencapsulated, tan to grey, unilocular or multilocular masses, occasionally with necrotic areas.

Histopathology Sheets, islands and nests are composed of large, round to polyhedral cells with fine, granular, eosinophilic cytoplasm and central, round vesicular nuclei, often with prominent nucleoli {257}. Occasionally there are multinucleated cells. In some tumours there are duct-like structures of variable calibre. They are unencapsulated and often invade muscle, lymphatics and nerves. They are characterised cytologically by cellular atypia and pleomorphism. Histochemically, phosphotungstic acidhaematoxylin (PTAH) staining reveals fine, blue, cytoplasmic granulues. Other methods to demonstrate mitochondria such as the Novelli technique, cresylecht violet V, Kluver-Barrera Luxol fast blue stains {2601} and antimitochondrial antibodies can also be used {2343}.

 Immunoprofile Ki-67 immunostaining has been suggested in separating benign from malignant oncocytoma {1188}. In addition, alpha-1- antitrypsin staining has been helpful {476}.

Electron microscopy There are large numbers of mitochondria which are often abnormal in shape and size. Intracytoplasmic lumina lined with microvilli and lipid droplets have also been reported. A nearly continuous basal lamina, evenly spaced desmosomes and rearrangement of mitochondrial cristae have been demonstrated {218}.

 Prognosis and predictive factors These high-grade tumours are characterised by multiple local recurrences and regional or distant metastases {922,940}. In one series, 7 of 11 patients studied ultimately developed metastatic disease {1227}. It appears that the most important prognostic indicator is the presence or absence of distant metastases {1833}.

Oncocytic carcinoma Fig. 5.23 Oncocytic carcinoma. A Invasion into the parotid gland. B Atypical tumour cells have prominent nucleoli and eosinophilic, granular cytoplasm. C Perineural invasion.