PRIMARY MUCOSAL MELANOMAS OF THE NASAL CAVITY AND PARANASAL SINUSES -A CLINICOPATHOLOGICAL ANALYSIS OF 14 CASES

We present 14 patients with primary sinonasal melanomas (SM) identifie d from 1984-1997 in our archives (11/14 lateral nose, 1/14 nasal septu m, 2/14 paranasal sinuses; 8M/6F mean age 67.7 years, range 39-88 year s). Survival was poor (median 9 months) with death related to extensiv e local disease and/or widespread hematogenous metastases. The followi ng histological subtypes were identified in descending order: amelanot ic small blue cell, pleomorphic, epithelioid. spindle cell and myxoid. High mitotic rate and vascular invasion, absence of tumor-infiltratin g lymphocytes and regression wen features shared by all SM. Negative s taining of B- and T-cell markers, LCA, neuroendocrine markers such as NSE, chromogranin and synaptophysin, and CK-negativity excluded olfact ory neuroblastoma, small cell undifferentiated carcinoma, and lymphoma . S-100 protein was expressed in all SM, but demonstrated variable sta ining intensity with areas of complete negativity. HMB45 was strongly and uniformly (>80%) expressed in all undifferentiated small blue cell SM. The pigmented SM were predominantly HMB45-negative. The strong HM B45 staining in amelanotic small blue cell SM is explained by the reac tion of HMB45 antibody with an oncofetal antigen found in immature mel anosomes. In these poorly differentiated amelanotic malignant melanoma s, antibody to HMB45 proved to be a superb diagnostic marker. We there fore strongly advocate the inclusion of HMB45 antibody in the panel of antibodies for initial work-up of undifferentiated mucosal neoplasms, since a negative S-100 stain in small biopsy material may result in i ncorrect classification of these neoplasms.