Anti-KBA.62 (Melanoma Associated Antigen) is a novel anti-melanoma antibody. Studies thus far have shown a similar sensitivity to melanocytic proliferations as that seen with S-100 protein staining, which is somewhat higher than that seen with anti-HMB-45. This has been confirmed by one study on a series of 215 sentinel lymph nodes. Moreover, anti-KBA.62 identified 6 patients (3%) who had confirmed sentinel lymph node metastasis but stained negative using anti-HMB-45. In this setting, the resolution appears to be higher than S-100 protein in that the staining pattern (membranous) is quite distinct. Interestingly, most cases of desmoplastic and spindle cell melanomas show strongly positive results with anti-KBA.62, unlike that seen with other melanocyte markers. It should be noted that anti-KBA.62 will label occasional endothelial cells which can serve as an internal positive control. A small percentage of well-differentiated squamous cell carcinomas of the skin (and lung) have also been noted to stain with this antibody; however, the poorly-differentiated forms of carcinoma do not, thus resolving a greater practical problem in differential diagnosis. Anti-KBA.62 is a useful additional marker for melanoma, specifically in desmoplastic/spindle cell cases and in the context of micrometastasis in sentinel lymph node.
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