Synthesis of alpha-fetoprotein by human yolk sac tumor transplanted into nude mice.

All nude mice bearing primary or secondary transplants of a human yolk sac tumor exhibited a high serum alpha-fetoprotein level. This finding clearly indicates the synthesis of alpha-fetoprotein by the human yolk sac tumor and supports an idea that human yolk sac tumor simulates yolk sac endoderm not only morphologically but also functionally.