[Desmoplastic recurrence of a melanoma of the female urethra]

We report a case of melanoma of the female urethra, recurring on the vulva as a desmoplastic invasive melanoma. The urethral tumor was an unclassifiable melanoma with an invasive epithelioid, and an intraepidermal atypical melanocytic component. The desmoplastic recidive was made of intersecting fascicles of spindled, moderately atypical cells, scattered over a dense collagenous matrix. Tumor cells were immunoreactive for S100 protein and vimentin, negative for HMB45. The morphological and immunophenotypic differences with the initial tumor, the absence of melanocytic dysplasia within the overlying epidermis, could lead to a misinterpretation of this lesion as a fibrous scar or a fibrohistiocytic tumor. Desmoplastic melanoma shares many homologies with acrolentiginous and mucous membrane melanoma and could occur more frequently on the genitourinary tract than it is generally assumed.