Inhibition of Urethan Lung Tumor Induction in Mice by Total-body X-radiation.

potent carcinogen capable of producing pulmonary tumors in 100 per cent of susceptible animals after a single injection (14, 19). Interest in urethan in our laboratory followed reports of its effects on bone marrow (18), and experimental evidence of its capacity to provide increased radioresistance in mice to x-radiation has been published (6). In the course of these and other experiments the ques tion of radiation sensitivity of urethan tumor in duction arose. Observations from several different experiments and certain theoretical considera tions led us to suspect that x-radiation might in hibit urethan pulmonary tumor induction. The experiments reported here show a marked suppres sion of pulmonary tumor formation when total body x-radiation (880 rad) was carried out either before or after a single intraperitoneal injection of urethan, which by itself evoked multiple tumors in 100 per cent of nonirradiated control animals.