Sinonasal malignant melanoma. A clinicopathologic and immunohistochemical study of 14 cases.

The clinical, light microscopic, and immunohistochemical features of 14 sinonasal malignant melanomas were studied to show their diverse morphologic appearance and distinction from therapeutically more amenable neoplasms that occur in this region. The tumors arose in 6 men and 8 women (median age, 70 years). Eleven patients died of disease 7 to 44 months (median, 18 months) after diagnosis. The absolute median survival time was 18.5 months (range, 7 to 44 months). The predominant microscopic appearance was categorized as small blue cell in eight cases, spindle cell in three cases, epithelioid in two cases, and pleomorphic in one case. Eight tumors had multiple patterns. Five sinonasal malignant melanomas had theque-like growth, five had junctional change, and 10 contained at least rare melanin pigment. Fourteen, 13, and 12 sinonasal malignant melanomas were immunoreactive with anti-vimentin, HMB45, and anti-S100 protein antibodies, respectively. One epithelioid tumor positive for vimentin, S100, and HMB45 also contained scattered epithelial membrane antigen-positive and cytokeratin-positive cells, which emphasizes the need for a battery of stains to distinguish sinonasal malignant melanoma from carcinoma. All tumors were negative for leukocyte common antigen, muscle-specific actin, and synaptophysin. Diffuse immunopositivity for vimentin, S100 protein, and HMB45 allows distinction of sinonasal malignant melanomas from histologically similar neoplasms.