[Yolk sac tumor by fetectomy in the rat: histopathological characteristics and histogenesis (author's transl)].

Experimentally induced yolk sac tumors in rats were investigated with special regard to morphological and histochemical characteristics. Pregnant rats whose fetuses were removed on the 12th day of gestation, developed tumors which were derived from fetal membranes left outside the uterus. Out of 119 operated rats which had been mated with syngenic males, 95 rats beared tumors, which were histologically yolk sac tumors (46 cases), adenocarcinomas (29 cases), choriocarcinomas (5 cases) and teratomas (69 cases). An early lesion of yolk sac tumor was observed as early as 3 weeks after the surgical procedure, and the sera from these tumor-bearing rats were positive for alpha-fetoprotein (AFP). Morphological features of both the induced tumors and the cultured tumor cell masses revealed a thick stroma consisting of a PAS-positive basement membrane-like material, which closely resembled Reichert's membrane of the parietal yolk sac in the normal placenta. The intracellular localization of AFP in cultured cells was investigated by immuno-electron microscopic method, and the reaction product for AFP was seen in the endoplasmic reticulum and Golgi complex. Histogenesis of the tumor is also discussed.