Complementary expression of melanosomal antigens and constant expression of pigment-independent antigen during the evolution of melanocytic tumours.

We have generated monoclonal antibodies (MoAbs) against melanosomal proteins (MoAb 1C11 and MoAb HMSA-1) and a cytoplasmic protein strongly synthesized in neoplastic melanocytes but not associated with melanogenesis (MoAb 7H11). An immunohistochemical study of paraffin sections showed that nearly 90% of epidermal neoplastic melanocytes, including melanomas, expressed 1C11 antigen, whereas this antigen was poorly preserved in dermal melanocytic cells except melanomas. HMSA-1 antigen was expressed in a complementary manner to 1C11 antigen, being found in dermal naevus cells but not generally in the epidermal regions, except for dysplastic naevi and melanomas. In contrast, 7H11 antigen was distributed in nearly 90% of melanocytic tumours except solar lentigo and lentigo maligna lesions. The failure of MoAb 1C11 to react with dermal melanocytes may reflect a subtle alteration in melanogenesis during tumour evolution. Overall, the combined use of MoAbs serves as an accurate diagnosis of melanocytic tumours, the pigment-independent MoAb 7H11 being particularly useful for amelanotic and metastatic lesions.