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

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 r ecognized melanocyte-specific melanosomal protein MART-1 in routinely proce ssed 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%) o f SN and MN, respectively, demonstrated positive stainings in more than hal f of their tumor cells, as compared with only 10 of 22 (45%) of the MM (P < .05). The majority of lesions in all 3 types of tumors showed a homogeneou s mode of staining, although MM tended to show a more heterogeneous pattern . A consistent pattern of stratification of staining with progressive desce nt into the dermis was not demonstrated in these tumors. Conclusion: MART-1 does not differentiate between SN, MM, and ordinary MN i n a consistent pattern, but it may be used as a marker for these tumors.