Diagnostic performance of melanocytic markers for immunocytochemical evaluation of lymph-node melanoma metastases on cytological samples.

Aims The diagnosis of metastatic cutaneous melanoma (CM) on lymph node fine needle aspiration samples may be challenging and usually requires confirmation by immunocytochemistry. However, the cytological material could be too scant to order a broad panel of markers. In this case, the pathologist is forced to choose the most advantageous antibodies. The most commonly used melanocytic markers include S100, Melan-A, HMB45 and SOX10 but their diagnostic yield on cytological samples has been poorly studied. The current work aimed to evaluate the diagnostic performance of melanocytic markers when applied to cell blocks obtained from fine needle aspiration cytology (FNAC) of lymph node metastases from CM. Methods S100, Melan-A, HMB45 and SOX10 were tested on cell block sections of 38 lymphnode metastases from CM diagnosed by cytology. A combined score was built to evaluate each immunostaining, considering the intensity of the staining and the percentage of stained neoplastic cells. Results S100 and SOX10 revealed a higher sensitivity (100%) than Melan-A and HMB45 for the diagnosis of metastatic CM. Furthermore, SOX10 emerged as the melanocytic marker with the best staining performance. Conclusion SOX10 has a 100% detection rate and the most easily interpretable staining pattern compared with other melanocytic markers. Therefore, it is strongly recommended that SOX10 is included in the minimal immunocytochemical panel for the diagnostic evaluation of lymph node FNAC in patients with suspected CM metastasis.