Reduction of N-nitroso-N-ethylurea-induced neurogenic tumors by X-radiation: a life-span study in rats.

Whole-body X-irradiation after neonatal injection with N-nitroso-N-ethylurea (ENU) significantly reduced the incidence of induced neurogenic tumors in inbred HMT rats kept for their complete life-span. After administration of 10 mg ENU/kg and 1.25 Gy X-radiation, the incidence of schwannomas but not of gliomas was reduced as compared to the incidence in rats given 10 mg ENU/kg only. In contrast, after administration of 4 mg ENU/kg, 1.25 Gy reduced the incidence of gliomas but not of schwannomas. Administration of 1.25 Gy alone induced a remarkably high incidence of rats with neurogenic tumors (20%). Latency of tumor detection was not significantly affected by radiation. Among the most frequently occurring nonneurogenic tumors, squamous cell carcinomas were reduced in incidence by treatment with ENU, 1.25 Gy X-radiation, or both combined. No treatment affected the incidence of pituitary or mammary tumors. There was a preponderance of ovarian tumors in rats given 4 mg ENU/kg + 1.25 Gy. An incidental finding was the occurrence of granular cell tumors in 7 rats from different treatment groups.