Trophoblastic tumors of the testis other than classic choriocarcinoma: "monophasic" choriocarcinoma and placental site trophoblastic tumor: a report of two cases.

We report two unusual forms of testicular trophoblastic tumor. One was a mixed germ cell tumor in a 19-year-old man that had a predominant component of nodules of cytotrophoblast cells with only rare syncytiotrophoblast cells. These nodules of "monophasic" choriocarcinoma were diffusely positive for human chorionic gonadotropin (hCG), which stained the syncytiotrophoblast cells more intensely; stains for human placental lactogen (HPL) highlighted only the latter cells. The second tumor occurred in a 16-month-old boy. It consisted of a pure proliferation of intermediate trophoblast cells and was identical to the placental site trophoblastic tumor of the uterus. The tumor cells showed diffuse immunoreactivity for HPL and patchy staining for hCG. Despite the occurrence of vascular wall invasion, the patient was alive and well at 8 years follow-up with no treatment other than orchiectomy. These cases show that trophoblastic tumors other than classic choriocarcinoma occur rarely in the testis. The differential diagnosis of the "monophasic" choriocarcinoma included seminoma and the solid variant of yolk sac tumor, but the tumor had larger, more irregular nuclei than those of seminoma and was not associated with distinctive yolk sac tumor patterns. The placental site trophoblastic tumor may be confused with Leydig cell tumor or choriocarcinoma, but awareness of its occurrence in the testis and the immunohistochemical findings should permit its recognition.