An assessment of “neuroendocrine differentiation” in malignant melanomas of the sinonasal and oral region

Mucosal melanomas often require a detailed differential diagnosis and immunochemical study due to their different morphology and pattern characteristics. The tumors may also show fibroblastic, schwannian, smooth muscle, rhabdomyosarcomatous, gangliocytic, epithelial, and neuroendocrine differentiation. All these features can lead to serious diagnostic difficulties. The study aimed to determine the frequency of neuroendocrine differentiation in melanomas of the sinonasal and oral regions and to assess whether there is any relationship between neuroendocrine differentiation and clinical, histopathological, and other immunophenotypic features of this neoplasm. The study included 18 cases diagnosed with oral or sinonasal malignant melanoma. Neuroendocrine differentiation was determined by immunohistochemistry using synaptophysin, chromogranin, CD56, and INSM-1. A cut-off defining neuroendocrine differentiation in malignant melanomas has not been established in the literature. Because of this, any degree of neuroendocrine marker expression was considered as indicative of “neuroendocrine differentiation” without setting any cut-off. Neuroendocrine differentiation was observed in 13 of 18 cases (72.2 %) when a single positive neuroendocrine marker was considered sufficient. The number of cases with at least two positive neuroendocrine markers was 8/18 (44.4 %). Synaptophysin, chromogranin A, CD56, and INSM1 were positive in 33.3 %, 13.3 %, 56.2 %, and 47.1 % of cases, respectively. The results of our study suggest that neuroendocrine differentiation is not uncommon in oral and sinonasal melanomas. Knowing that malignant melanomas can show neuroendocrine differentiation will prevent diagnostic pitfalls.