testicular germ cell tumor (tes-TIH-kyoo-ler jerm sel TOO-mer)
A type of tumor that forms in a testicle from germ cells (cells that make sperm). Two main types of testicular germ cell tumors are seminomas and nonseminomas. Seminomas grow and spread slowly and are sensitive to radiation therapy. Nonseminomas grow and spread more quickly than seminomas. There are several different types of nonseminomas.