Effects of major histocompatibility complex (RT1) and timing of fetectomy upon experimental induction of yolk sac tumor, choriocarcinoma, and teratomas in the rat.

Suitable conditions for inducing experimental yolk sac tumor (YST), choriocarcinoma and teratomas by simple fetectomy were studied in the rat. Tumors were inducible only when fetectomy was performed between the 7th and 14th gestational day. No YST was induced by fetectomy performed after the 15th gestational day. RT1 (major histocompatibility complex of rat) compatibility was also required for the YST induction and no tumor was induced in RT1-incompatible combinations. Only 39% of fetectomized rats produced YST after mating between an inbred strain and their backcrossed F1 hybrid. Mean survival time of the tumor-bearing rats fetectomized on the 10th gestational day was 116 days. The mean diameter of the tumor was maximum in the group fetectomized in the 9th gestational day, and minimum in the group fetectomized on the 14th gestational day.