Kba.62 and S100 protein expression in cytologic samples of metastatic malignant melanoma

The diagnosis of melanoma can be challenging, especially in metastatic lesions, due to the ability of melanoma cells to morphologically mimic carcinoma, sarcoma and even lymphoma cells. Moreover, melanomas can exhibit negative immunostaining for the melanoma markers HMB-45 and MART-1/Melan-A, often used in the diagnosis of this tumor. KBA.62 is a recently described antibody that reacts with benign and malignant melanocytic proliferations. In this study, we report our experience with KBA.62 and S100 protein immunostaining in the diagnosis of metastatic melanoma on fine-needle aspiration and effusion samples. We reviewed 60 cytology samples from 58 patients with metastatic melanoma. Our results showed that KBA.62 stained 75% of the cases and S100 protein 87% of the cases. KBA.62 and S100 protein stained the majority of metastatic melanomas that were negative for HMB-45 and MART-1; KBA.62 stained 73% of the cases and S100 protein 73% of the cases. The majority (85%) of the cases negative for HMB-45 and MART-1 were positive for KBA.62 and/or S100 protein. Additionally, we also observed that KBA.62 staining was positive in the majority of epithelioid and spindle cell type melanoma cells. In conclusion, the performances of KBA.62 and S100 protein were similar and both markers are useful in the diagnosis of metastatic melanoma in cytology material, especially when the tumor cells lack expression of HMB-45 and MART-1.