[Case of metastatic malignant melanoma of the urinary bladder]

A 54-year-old woman underwent resection of malignant melanoma of the left leg and inguinal lymph node metastases and subsequent radiation therapy (60 Gy) following three courses of dacarbazine, nimustine, vincristine and interferon-beta chemotherapy in January 2010. In September 2011, she was referred to our department with the chief complaint of asymptomatic gross hematuria. A non-papillary bladder tumor was detected on cystoscopy and fluorodeoxyglucose (FDG) positron emission fomography-computed tomography revealed increased uptake of FDG only in the area of the bladder tumor. Melanoma cells were also found on urinary cytology. Our diagnosis was metastatic malignant melanoma of the bladder. Complete transurethral resection of the bladder tumor was performed, and pathological examination confirmed metastatic malignant melanoma. Metastatic bladder tumors constitute less than 5% of all bladder tumors. There are metastases in other organs at the time of diagnosis in almost all cases. In Japan, metastatic malignant melanoma of the urinary bladder is rare in clinical practice, there having been about a dozen reported cases. Solitary metastasis as in our case is even rarer.