Viral-versus non-viral-induced yolk sac tumors in the rat.

Yolk sac tumors were induced in fetectomized rats by displacement of the visceral yolk sac outside the uterus with or without injection of murine sarcoma virus (MSV) into the placenta. Some of the animals were immunized with MSV prior to surgery. The biological, morphological and immunological characteristics of the tumors which develop in animals either injected or not with virus are compared. The results indicate that MSV inoculation into the placenta increases the tumor incidence, shortens the latency period, and induces, apart from yolk sac carcinoma (YSC), less differentiated tumors (embryonal cell carcinoma, EC). The transplanted and/or in vitro cultured YSC derived from primary tumors obtained in animals either injected or not with MSV show the same morphology, are not immunogenic, secrete alphafetoprotein and express endodermal antigen.