The effect of x-radiation given after neonatal administration of ethyl nitrosourea on incidence of induced nervous system tumours.

Neonatal rats were injected with neurocarcinogenic amounts of ethyl nitrosourea (ENU) and whole-body X-irradiated 24 h later. An absorbed radiation dose of 1.25 Gy caused a statistically significant decrease in the incidence of nervous system tumours induced by ENU (10 mg/kg). Absorbed doses of 0.2 Gy or 1.25 Gy given after ENU (4 mg/kg) also reduced their incidence, but not significantly so. The X-irradiation did not affect the range of histological appearances amongst the tumours but malignant schwannomas, particularly those of the trigeminal nerve, were significantly reduced by 1.25 Gy given after ENU (10 mg/kg). The mean latency for clinical signs of tumour appearance was not affected by radiation. A small number of nervous system tumours occurred in rats given neonatal X-radiation only and it seems highly likely that these were radiation-induced.