Ultrastructural studies of xenografted human germ cell tumors.

Xenografts have been established in immune-suppressed mice from three embryonal cell carcinomas, two yolk sac carcinomas, and a 'seminoma-like' tumor that produces alphafetoprotein. The ultrastructural features of these xenografts have been studied in detail and compared with human germ cell tumors removed from patients. A spectrum of ultrastructural differentiation has been demonstrated for tumors of the same histologic classification (embryonal cell carcinoma) and within individual tumors. Cells with ultrastructural appearances intermediate between seminoma and yolk sac carcinoma and between embryonal cell and yolk sac carcinoma have been demonstrated, and their potential implications for tumor histogenesis are discussed.