Testicular germ cell tumor (TGCT) comprises about 98% of all testicular neoplasms and is thereby the most common malignancy among young males. Overall, three different entities of TGCT can be distinguished: teratomas and yolk sac tumors of newborns and infants, seminomatous and nonseminomatous germ cell tumors of adolescents and young adults, and spermatocytic seminoma of elderly men. Recent studies of TGCTs have suggested that overexpression of cyclin D2 is a very early, possibly the oncogenic, event in GC tumorigenesis.