Thought to have its origin in the testes, with involution of the primary tumor accounting for the appearance as an extragonadal lesion.
Cumulative 10 year risk of developing metachronous testicular cancer for patients with extragonadal germ cell tumors is 10.3%.
Testicular germ cell tumors-with extragonadal tumors of the retroperitoneum an nonseminomatous cell type there is a 14.3% 10 year risk for development of metachronous testicular cancer.