Testicular non seminomatous germ cell tumor describes a group of testicular germ cell tumors (see this term) occurring in the third decade of life (mean age: 25 years) with a usually painless unilateral mass in the scrotum or in some cases with gynaecomastia and/or back and flack pain and characterized by a more aggressive clinical course than testicular seminomatous germ cell tumors (see this term) with rapid involvement of blood vessels and a poorer prognosis. Histologically, they can be either undifferentiated (embryonal carcinoma), differentiated (teratoma, yolk sac tumor, choriocarcinoma), or can consist of a mixture of seminomatous and nonseminomatous components.