Small cell carcinoma of the major salivary glands: clinicopathologic study with emphasis on cytokeratin 20 immunoreactivity and clinical outcome.

Small cell carcinomas arising in salivary glands, extremely rare high-grade malignant tumors, are subclassified into neuroendocrine and ductal types. The neuroendocrine type may be segregated further into Merkel cell and pulmonary varieties according to cytokeratin 20 immunoreactivity. Whether subclassification of this tumor group has any biologic or clinical significance is not known. We examined 15 cases (11 men, 4 women; mean age, 66.5 years) of small cell carcinoma of major salivary glands from a single institution and analyzed their clinicopathologic profiles, including immunohistochemical features and prognostic factors. Three fourths of small cell carcinomas showed cytokeratin 20-positive immunostaining, often with a paranuclear dotlike pattern of reactivity. All tumors were immunoreactive for at least 2 of 6 neuroendocrine markers examined, and 6 tumors were also positive for neurofilament, with a paranuclear dotlike pattern. Postoperatively, 9 patients developed metastatic disease, and 10 patients died of disease 2 to 45 months (mean, 15.9 months) after diagnosis. By log-rank analysis, overall survival was reduced significantly for patients with a primary tumor larger than 3 cm in diameter (P = 0.032), negative immunostain reaction for cytokeratin 20 (P = 0.012), and decreased immunoreactivity for neuroendocrine markers (P = 0.034). These results indicate that small cell carcinoma of major salivary glands is a highly aggressive tumor, although the prognosis may be better than for extrasalivary neoplasms. Our data also suggest that most salivary gland small cell carcinomas exhibit neuroendocrine differentiation. Immunohistochemical expression of cytokeratin 20 can be used to classify salivary small cell carcinomas into Merkel cell and pulmonary types and may have prognostic significance.