Narida Chirakalwasan, M.D.*
* Department of Anatomical pathology, Maharat Nakhon Ratchasima Hospital
E-mail :



Primary sinonasal mucosal melanoma is a rare neoplasm. Like in other sites of malignant melanoma, the histopathology is variable and when lacking of melanin pigment, particularly in small biopsy specimen mimicks many neoplasms. Immunohistochemical staining plays an important role. Many immunomarkers, including S-100, HMB-45 and Melan-A should be included in a panel of immunohistochemistry to increase the sensitivity of detection of melanocytic differentiation, particularly in sinonasal region. Furthermore, expression of several aberrant immunophenotypic markers in malignant melanoma should be aware of in order to prevent misdiagnosis. This is an unusual case of sinonasal mucosal melanoma in a 50-year-old male, showing plasmacytoid appearance with CD138 expression. The tumor was also focally and weakly positive for S-100 immunostaining. These findings may lead to wrong diagnosis of plasma cell neoplasm.