A case of a solitary melanocytic renal tumor with no apparent primary lesion or metastasis is reported. Pathologically the tumor was composed of cells with brown pigmentation that strongly reacted to monoclonal antibody HMB-45 immunohistochemically. Few mitotic figures, mild nuclear atypia and nucleolar prominence were observed. These findings confirmed that the tumor cells were melanogenetic but the malignant potential of the tumor was low in comparison to that of typical malignant melanoma. The patient is doing well 44 months after partial resection of the renal tumor and postoperative chemotherapy. The interesting pathological feature may account for the unique clinical course.
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