Experimental yolk-sac tumors produced by fetectomy without virus infection in rats.

Pregnant WKA rats were laparotomized on the 12th day of gestation, and all fetuses were removed from the uteri, leaving the fetal membranes attached to placentas in situ, protruding into the peritoneal cavity. After 5 to 6 months, extrauterine tumors were observed in 80% of the operated rats, and elevated serum alpha-fetoprotein levels were detected in 80% of the tumor-bearing rats. The tumors in AFP-positive rats always contained yolk-sac tumor elements. In transplantable tumor lines established in the ascites form, numerous free-floating embryoid bodies were observed. The experiments demonstrate that yolk-sac tumors (endodermal sinus tumors) can be induced by simple fetectomy without infection by exogenous tumor virus.