The melanoma-specific XMEL antigen is expressed in dysplastic naevi

We have previously shown that a novel monoclonal antibody, XMEL, exhibited reactivity with deep primary melanomas while showing no reactivity with other tumours and normal tissue. XMEL was raised against a part of the extracellular domain of Xmrk, a growth factor receptor presumed to mediate melanoma formation in the Xiphophorus fish model. Here we investigate the range of XMEL immunohistochemical reactivity in paraffin sections from human common acquired and dysplastic naevi of both junctional and compound type. The strongest reactivity was observed with the compound dysplastic naevi. We conclude that the antigen recognized by XMEL acts early in the cascade of genetic alterations underlying progression into malignant melanoma. Our results also support the notion that the dysplastic naevus may play a role in progression of human malignant melanoma and may indeed represent the precursor stage.