KBA.62: a useful marker for primary and metastatic melanomas

SummaryWe previously described a novel antimelanoma antibody, designated KBA.62. However, review of the literature showed that only a few studies have reported on this antibody. We report our experience in the diagnosis of melanoma using KBA.62 and its value in both primary and metastatic conditions. In addition to conventional melanomas, we included desmoplastic and spindle cell melanomas, whose diagnosis can be challenging. We also focus on identification of malignant cells in sentinel lymph node biopsies using KBA.62, by comparison with anti–S-100 protein and HMB-45 antibodies, because discrepancies in sensitivity and specificity of melanoma markers have given rise to numerous studies aiming to determine the best panel for the evaluation of sentinel lymph node from patients with melanoma. Overall, KBA.62 was positive in 93% of primary and metastatic melanomas. Interestingly, the 12 cases of desmoplastic and spindle cell melanomas had strongly positive results. In addition, the results of our study performed on a series of 215 sentinel lymph nodes showed that the sensitivity of anti–S-100 protein and KBA.62 antibodies in detecting occult metastasis was similar. Moreover, KBA.62 identified 6 patients (3%) who had confirmed sentinel lymph node metastasis but were negative for HMB-45. The resolution was higher with KBA.62 than that observed with anti–S-100 protein antibody, as the nonmelanocytic positive cells for KBA.62 in lymph nodes were only represented by endothelial cells, which therefore constituted an intrinsic positive control. We conclude that KBA.62 antibody is a useful additional marker for melanoma, specifically in desmoplastic/spindle cell cases and in the context of micrometastasis in sentinel lymph node.