Melan-A as a useful diagnostic immunohistochemical stain for the diagnosis of primary sinonasal melanomas.

Background Sinonasal melanomas are rare neoplasms whose diagnosis may require confirmatory immunohistochemical stains. S-100 protein and HMB-45, the stains most commonly used, have varying sensitivities and specificities. Melan-A, a more recent melanoma-specific marker, may prove helpful when S-100 protein and HMB-45 stains are negative or equivocal. Methods Seven cases of sinonasal melanoma were assessed for reactivity with Melan-A, S-100 protein and HMB-45. Results The study group consisted of two women and five men ages 40 to 83. Six of the neoplasms were strongly positive for S-100 protein. One case was negative for S-100 protein and HMB-45 but positive for Melan-A. HMB-45 staining varied between diffusely positive (three cases), focally positive (two cases), and negative (two cases). All cases were positive for Melan-A either diffusely (four cases) or focally (three cases). Conclusion Because Melan-A can be positive in cases that are S-100 protein or HMB-45 negative, it is a useful component in the immunohistochemical panel for the diagnosis of sinonasal melanomas. © 2002 John Wiley & Sons, Inc. Head Neck 24: 52–55, 2002.