The origin of germ cell tumors of the testis.

Two hundred and eight cases of germ cell tumors of the testis were thoroughly studied. Fifty-one (24.5%) were embryonal carcinoma, 115 (55.3%) were seminoma, and 42 (20.2%) contained both embryonal carcinoma and seminoma. The average age of the patients with embryonal carcinoma, seminoma, and combined tumors was 27.6, 38.3, and 30.3 years. Furthermore, in the patients with combined tumors, those having a predominance of embryonal carcinoma had an average age of 28.3 years, while those having a predominance of seminoma had an average age of 33.4 years. This study supports the concept that the malignant potential of germ cells in younger patients is embryonal carcinoma, the malignant potential of germ cells in older patients is seminoma, and that in intermediate-aged patients the germ cells are capable of developing varying amounts of embryonal carcinoma and seminoma in the same tumor.