Testicular teratoma with nephroblastoma component.

We report the development of Wilms' tumor in an atrophic testis and review the potential molecular pathogenesis. An 18-year-old man presented with 2 days of right testicular pain and growth in his atrophic testis. Ultrasonography revealed a heterogeneous mass. The chest radiographic findings and testicular tumor marker levels were normal. He underwent radical orchiectomy, with the pathologic examination showing teratoma with a nephroblastoma component, focal embryonal carcinoma, and minute yolk sac tumor. The development of Wilms' tumor in the testis is rare and can be explained by the activation of the WT1 gene during embryogenesis.