[Experimental teratoma derived from mouse yolk sac (author's transl)]

By using no carcinogens, well differentiated teratomas were induced by BALB/c nu/+, +/+ and ICR strain of mice. On the 11th to 18th day of gestation, mice were laparotomized and all fetuses were removed from uterus, leaving placentas in situ and fetal membranes were protruded into peritoneal cavity. After 5 to 139 days of operation, extrauterine tumors developed in twenty five mice of fifty fetectomized mice. In BALB/c nu/+ mice the tumor developed in six of ten, in +/+ mice eighteen of twenty five and in ICR mice only one of fifteen. The tumors were all histologically well differentiated teratomas, some contained tissues derived from one germ layer and other from two or three germ layers but no undifferentiated cells. The teratomas became cystic, so we call, endodermal cysts on histological examination during rather long term observations. We concluded that these induced tumors were not genuine tumors in real pathologic means but only well differentiated tissues derived from the yolk sac on developmental stage. Alpha-fetoprotein (AFP) in serum or in cystic contents of the tumor bearing mice were not detected by double immunodiffusion method.