The Xiphophorus-derived antibody, XMEL, shows sensitivity and specificity for human cutaneous melanoma but is not a prognostic marker.
XMEL is a monoclonal antibody raised against part of the extracellular domain of the putative tyrosine kinase receptor protein implicated in the pathogenesis of melanoma formation in the Xiphophorus fish melanoma model. Our objective in this study was to determine the diagnostic and prognostic utility of XMEL for human melanoma. Formalin-fixed tissue from 82 melanomas, 42 carcinomas, 23 neural tumors, 12 lymphomas and 12 sarcomas were immunostained with XMEL and compared with a widely used melanoma antibody, HMB-45. The sensitivity of HMB-45 (83.1%) was similar to that of XMEL (79.8%). XMEL detected 7 melanomas that were HMB-45 negative. Specificity for detection of melanoma was greater with HMB-45 (95.5%) as compared to XMEL (80.9%). Of interest, all 4 prostatic adenocarcinomas were XMEL positive. These data suggest that XMEL is as sensitive but not as specific as HMB-45 in the detection of cutaneous melanoma but may serve as an ancillary antibody to improve diagnostic yield. The consistent positivity of XMEL in melanoma lends support to the hypothesis that the detected protein plays a role in melanoma pathogenesis. XMEL reactivity is not an independent prognosticator of death from melanoma in 37 melanomas from patients with at least 10 years' follow-up. These data and the fact that XMEL shows variable reactivity with metastatic melanomas but almost 100% reactivity with the primary melanomas suggest that the antigen recognized by the XMEL antibody may be important in the early stages of melanoma progression. This is supported by our earlier observation that XMEL is reactive with dysplastic nevi, a precursor of malignant melanoma.