Dysplastic melanocytic nevus. Immunohistochemical heterogeneity by melanosomal markers and S-100.

This study evaluates the expression of human melanosome specific antigen-1 and -2 (HMSA-1, -2) by dysplastic melanocytic nevus (DMN) and its significance by (a) immunostaining pattern, (b) other immunohistochemical markers (e.g., S-100), and (c) mesenchymal responses (e.g., lymphocytic infiltration). From 31 patients with DMN syndrome, 55 clinically characteristic and histologically (H&E) proven dysplastic nevi were assessed for HMSA expression. Approximately 70% of DMN lesions expressed the HMSA antigens; similar gross staining patterns were seen with both monoclonal antibodies (MoAbs). The expression of HMSA-2 was invariably associated with that of HMSA-1, but the converse did not apply. Two general staining patterns with MoAbs HMSA were appreciated: (a) uniform staining of the epidermal melanocytes in the DMN lesion (type I) and (b) nonuniform staining, with the epidermal melanocytes at the periphery of the DMN lesion reacting most intensely (type II). Although anti-S-100 antibody demonstrated a similar sensitivity (67%), it lacked specificity and did not distinguish different types of DMN, as compared with MoAbs HMSA. There was no correlation between these observed staining patterns and common histological features of DMN. There was a poor correlation between lymphocytic infiltrate (as judged by immunostaining for pan-T, Ti/h, Tc/s, and pan-B markers) and heterogeneity of immunostaining. We conclude that HMSA-1 and -2 are able to delineate two types of DMN and possibly bind different epitopes of the same antigen. Their potential usefulness in predicting malignant transformation of DMN has yet to be established.