Expression of melanocytic differentiation markers in malignant melanomas of the oral and sinonasal mucosa

Malignant melanomas of the oral and sinonasal mucosa are rare tumors. Amela notic variants can, on occasion, be difficult to recognize by routine light microscopy. Immunohistochemical studies may be needed for a final diagnosi s. A number of new monoclonal antibodies to melanocytic differentiation ant igens have been studied recently on primary cutaneous and metastatic melano ma. However, little is known about these antibodies for the diagnosis of mu cosal melanomas. In this study the authors analyzed 79 oral and sinonasal m ucosal melanomas of 65 patients. A total of 35 tumors originated from the o ral mucosa (21 primary tumors, eight local recurrences, and six metastases) and 44 melanomas were from the sinonasal tract (27 primary tumors, nine lo cal recurrences, and eight metastases). Immunohistochemical studies were pe rformed on paraffin-embedded tissues, using the following antibodies: anti- S-100 protein, T311 (anti-tyrosinase), A103 (anti-Mart-1/Melan-A), D5 (anti microphthalmia-associated transcription factor), and HMB-45 (anti-gp100). O f 35 oral mucosal tumors, 34 (97%) were positive with anti-S-100 protein, 3 3 (94%) with T311, 30 (85%) with A103, 26 (74%) with D5, and 25 (71%) with HMB-45. All five desmoplastic melanomas of the oral mucosa were positive fo r S-100 protein, four for tyrosinase, and one each for HMB-45 and A103. No desmoplastic melanoma was positive with D5. All 44 sinonasal melanomas were positive for tyrosinase and Mart-1/Melan-A (100%). Forty-three (98%) were positive with HMB-45, 42 (95%) with anti-S-100 protein, and 40 (91%) with D 5. These results reveal that T311 is the most sensitive marker for sinonasa l melanomas and closely approaches the sensitivity of anti-S-100 protein fo r oral mucosal melanomas. For desmoplastic mucosal tumors, anti-S-100 prote in remains the most sensitive marker.