Primary Mucosal Melanoma Mimicking High Grade Urothelial Carcinoma: A Potential Diagnostic Pitfall

Primary malignant melanomas of the genitourinary tract are rare, representing < 1% of all cases of melanoma1,2. We report a case of a 68-year-old female patient with primary malignant melanoma of the urethra with morphology mimicking that of high grade papillary urothelial carcinoma. The patient presented following a workup with an outside urologist that revealed a urethral mass. The patient complained of urinary incontinence and pelvic pain at initial presentation. A CT scan of the abdomen & pelvis revealed a soft tissue density within the vaginal vault, consistent with urethral cancer. A cystoscopy and urethral excisional biopsy was performed. Histologic examination of the specimen revealed an invasive tumor composed of epithelioid cells with prominent eosinophilic cytoplasm forming papillary structures. However, the tumor cells were negative for CK7, CK20, GATA 3 and Pancytokeratin and positive for S-100, SOX 10 and Melan A. The case was ultimately diagnosed as malignant melanoma.