A103 - AN ANTI-MELAN-A MONOCLONAL-ANTIBODY FOR THE DETECTION OF MALIGNANT-MELANOMA IN PARAFFIN-EMBEDDED TISSUES

Melan-A is a previously defined, melanocyte differentiation antigen, a nd an anti-Melan-A murine monoclonal antibody, A103, was recently deve loped by our group. In this study, we evaluated A103 immunoreactivity on formalin-fixed, paraffin-embedded tissues, exploring the potential of A103 in the diagnosis of metastatic melanoma. Seventy-five metastat ic melanomas, 10 primary melanomas, and 10 benign melanocytic nevi wer e tested. The reactivity of A103 was compared with HMB-4, an anti-gp10 0 antibody. Results showed that all nevi were A103 positive, and most primary melanomas were A103 and HMB45 positive. Of 75 metastatic melan omas, 61 (81%) were A103 positive, and 56 (75%) were HMB45 positive. O f 19 HMB45-negative lesions, 8 were A103 positive; of 14 A103-negative lesions, 3 were HMB45 positive. Eleven metastatic lesions, as well as 2 of 10 primary melanomas, were dual negative. These negative cases c onsisted mainly of the spindle cell and desmoplastic variants. Of the positive cases, A103 showed homogeneous staining in a significantly hi gher proportion of cases than HMB45 (72% versus 52%). In addition, foc al staining with less than 5% reactive tumor cells was seen more frequ ently in HMB45 (12 of 56) than in A103 (5 of 61). These results indica ted that A103 can be used as a first-line antibody in the diagnosis of metastatic melanoma. Our results also showed that A103 reacted with a ngiomyolipoma, which is known to be HMB45 positive. Of normal tissues, unexpected A103 reactivity was observed in the adrenal cortex, granul osa and theca cells of the ovary, and Leydig cells of the testis. This A103 immunoreactivity in benign and neoplastic tissues of nonmelanocy tic origin, the basis of which is unclear, could also be of potential diagnostic value.