Diagnosis: Malignant melanoma of the urothelial tract
• Most melanomas affecting the urinary tract are metastatic. Primary malignant melanomas of the urinary tract are rare and are diagnosed after exclusion of metastatic disease.
• Primary urethral melanomas have been described in men and women. Demonstration of an associated in situ component favors it to be primary at this site; however, this can be difficult, because urethral melanomas are often large and ulcerated at the time of presentation.
• Urethral melanomas are aggressive tumors, which metastasize widely; metastases to inguinal and pelvic lymph nodes, as well as hematogenous metastases to liver, lungs, and brain, are not uncommon.
• Histologically malignant melanoma of the urethra shares the same histologic spectrum as the more common cutaneous melanoma.
• The main differential diagnosis could be extra-mammary Paget disease; however, immunohistochemical demonstration of S100 and HMB45, which are negative in Paget disease, are helpful in establishing the diagnosis.
