Primary Mucosal Melanoma of the Sinonasal Tract: A Clinicopathologic and Immunohistochemical Study of Thirty-Two Cases

Sinonasal mucosal melanoma is a rare disease with poor survival. These tumors may have associated intraepithelial melanocytic proliferations, which are not extensively characterized. This retrospective analysis of 32 patients with sinonasal mucosal melanoma examined associated intraepithelial melanocytic proliferations in the context of diagnostic and prognostic features. Patient age ranged from 30 to 90 years (median 71) with a male to female ratio of approximately 3:2. Follow up for 31 patients ranged from 5 to 211 months (mean 42 months). Most patients died from melanoma-associated causes (18/31, 58 %), six (19 %) died from unknown causes, two (6 %) were alive with metastatic disease, and only five patients (16 %) remained alive without melanoma. The tumors were histopathologically heterogeneous, displaying epithelioid, spindled, and small cell cytomorphology. The presence of >2 mitoses/mm² and necrosis correlated with tumor progression and overall survival, respectively (p = 0.04 for both). Melanoma in situ, defined as a confluent intraepithelial proliferation of cytologically atypical melanocytes, was identified in 20 of 30 evaluable cases (67 %) and confirmed with immunohistochemical staining for microphthalmia-associated transcription factor. Melanocytic hyperplasia, defined as intraepithelial melanocytic proliferation without confluent growth or marked atypia, was seen in five cases (16 %). This incidence of associated intraepithelial melanocytic proliferations (83 %) is higher than previously reported. Because of the locally aggressive nature of these tumors, an awareness of the high rate of associated intraepithelial melanocytic proliferations may inform future studies of therapeutic options.