An aggressive malignant tumor arising from trophoblastic cells. The vast majority of cases arise in the uterus and represent gestational choriocarcinomas that derive from placental trophoblastic cells. Approximately half of the cases develop from a complete hydatidiform mole. A minority of cases arise in the testis or the ovaries. There is often marked elevation of human chorionic gonadotropin (hCG) in the blood. Choriocarcinomas disseminate rapidly through the hematogenous route; the lungs are most frequently affected. --2004