Primary malignant melanoma of the urinary bladder: clinical, morphological, and molecular analysis of five cases.

The aim of our study was to evaluate the clinical and morphological features of primary malignant melanomas of the urinary bladder. We obtained information on five such cases from three different institutions. These were three men and two women between 52 and 76 years of age. Three tumors presented with hematuria, one with dysuria, and one was discovered incidentally on imaging studies. All were invasive to muscularis propria on transuretral resections performed for diagnosis. Neoplastic cells showed variable patterns (large cell epithelioid, small cell diffuse, storiform, or mixed) in different tumors. Pigmentation was prominent in all except one case. Each case was labeled diffusely for S-100, HMB-45, and Melan-A. Pan-cytokeratin showed a perinuclear dot-like reaction in two tumors. Three cases showed the BRAF mutation in molecular studies. Two patients were already metastatic at the time of diagnosis. Two patients died, one is alive with disease after 15 months, and two patients are disease free at 1 and 5 years of surveillance.