Clear cell melanoma of the bladder.

Primary malignant melanoma of the urinary bladder is a rare tumor. A case in a 34-year-old man who presented with gross hematuria is reported. Cystoscopic biopsy showed a mixed spindle cell and clear cell neoplasm with focal pigmentation. The tumor cells were immunoreactive for S-100 protein and HMB-45. The patient did not have a history of melanoma, and clinical and radiologic work-up did not reveal other lesions, so a partial cystectomy and pelvic lymphadenectomy were performed. The tumor formed an ulcerated mass that extended into the perivesicular fat. Microscopically, the tumor was composed predominantly of clear cells in sheets or small nests. A solitary metastatic focus was present in 1 of 25 pelvic lymph nodes. Ultrastructurally, the tumor cells were characterized by irregular nuclear contours, complex nucleoli, abundant cytoplasmic glycogen, and premelanosomes.