EXPRESSION OF MELAN-A (MART1) IN BENIGN MELANOCYTIC NEVI AND PRIMARY CUTANEOUS MALIGNANT-MELANOMA

The Melan-A (MARTI) gene encodes an antigen recognized by cytotoxic T cells. Although its expression in metastatic melanoma has been documen ted in the literature by several investigators, little is known about its distribution in primary melanomas and benign melanocytic nevi. in this study, we evaluated Melan-A expression immunohistochemically on s ections from paraffin-embedded material of 50 benign nevi and 40 prima ry cutaneous melanomas using the monoclonal antibody A103. To evaluate a potential role of A103 in the differential diagnosis of melanocytic from nonmelanocytic tumors, we also analyzed a number of benign and m alignant peripheral nerve sheath tumors, fibrohistiocytic tumors, and leiomyosarcomas. Immunoreactivity with A103 was present in all ''nonne urotized'' nevi and in all nondesmoplastic primary melanomas, both in the intraepidermal and the dermal component. Only two nevi that underw ent prominent neurotization showed no staining with A103. Although all melanomas with epithelioid cells tended to be strongly positive with A103, only 4 of 13 spindle cell and desmoplastic melanomas (all positi ve with anti-S-100 and negative with HMB-45) were immunoreactive with A103 (two focally, two diffusely). None of the nonmelanocytic lesions expressed Melan-A. Our results confirm that Melan-A protein is broadly expressed in the majority of benign and malignant melanocytic lesions and suggest that A103 can be helpful diagnostically, not only for met astatic tumors, but also for primary skin lesions. Its use in distingu ishing between melanocytic and peripheral nerve sheath tumors, however , is limited because of the low or absent expression of Melan-A in nev i that underwent neurotization and spindle cell and desmoplastic melan omas.