[Experimental yolk sac tumors in the rat (author's transl)].

A study on the experimentally induced yolk sac tumor in the rat was made in special regard to the characteristics and origin of tumor cells. Pregnant rats which fetuses were removed on the 12th day of gestation, developed tumors derived from the fetal membranes left outside the uterus, which were composed of differentiated teratomas and yolk sac tumors. Serial observation of the oncogenesis revealed that an early lesion of the yolk sac tumor appeared in a nodule found as early as 3 weeks after the fetectomy and production of alpha-phetoprotein (AFP) was observed histochemically in the tumor cells 5 weeks after the fetectomy. A cultured cell line established after cloning from the transplantable yolk sac tumor which had been induced similarly and converted into ascitic form was also investigated. Light and electron microscopic studies on both induced tumors and the cultured cells indicated a similarity of AFP producing tumor cells with parietal yolk sac cells and of PAS-positive hyaline-like substance with the Reichert membrane. It is reasonable to conclude that the yolk sac tumor observed is regarded as a parietal yolk sac carcinoma described by Pierce. Histogenesis of the tumor is also discussed.