A comparative immunohistochemical study of MART-1 expression in Spitz nevi, ordinary melanocytic nevi, and malignant melanomas ☆

Abstract Background: The histopathologic differential diagnosis of Spitz nevus (SN) from malignant melanoma (MM) may be difficult. Objective: We attempted to elucidate the pattern of expression of a newly recognized melanocyte-specific melanosomal protein MART-1 in routinely processed specimens of SNs, MMs, and ordinary melanocytic nevi (MNs) and to see whether it can help to differentiate between them. Methods: Twenty SN, 22 MM, and 27 ordinary MN were immunostained with anti-MART-1 monoclonal antibody (clone A103). Results: All SNs, MNs, and MMs demonstrated cytoplasmic staining for MART-1 in some of their tumor cells, of which 17 of 20 (85%) and 24 of 27 (89%) of SN and MN, respectively, demonstrated positive stainings in more than half of their tumor cells, as compared with only 10 of 22 (45%) of the MM ( P Conclusion: MART-1 does not differentiate between SN, MM, and ordinary MN in a consistent pattern, but it may be used as a marker for these tumors. (J Am Acad Dermatol 2000;42:496-500.)