Malignant melanoma of the female urethra

Backgrounds: Malignant melanoma (MM) of urethra is extremely rare; only 84 cases have been reported in PubMed search. Case: An 84-year-old woman presented dysuria. Physical and endoscopic examination revealed a polypoid tumor in proximal urethra, and endoscopic tumorectomy was performed. The tumor could not be seen in outer genitalia. Grossly, the tumor is brownish soft tumor measuring 15 mm × 26 mm × 23 mm. Multiple sections were made and immunohistochemical procedures were performed. Microscopically, malignant epithelioid cells with brown pigment were seen to proliferate and invade. The size of tumor was circa 13 mm × 21 mm × 18 mm. The depth of invasion was 10 mm (pT4), but it was not clear whether the marginal tissue status is positive or negative. Lymphovascular permeation seen, yet no obvious vascular invasion was noted. The brown pigment was found to be melanin by Masson-Fontana stain. Immunohistochemical study showed tumor cells were positive for vimentin, S100 protein, HMB45, Melan A, p53, and Ki67 (labeling = 85%), KIT and PDGFRA, while they were negative for cytokeratins. Genetic analysis of paraffin-embedded tumor tissue identified no mutations in hot spots of KIT and PDGFRA genes. No apparent metastatic lesions were seen after the diagnosis. The outcome of the patient is unknown because the patient was referred to a large hospital specializing in cancer treatment. Conclusions: The author presented a very rare case of MM of the proximal urethra. The MM showed typical histochemical and immunohistochemical features. No mutations of KIT and PDGFRA were seen.