Abstract
α‐Difluoromethylornithine (DFMO) is an inhibitor of putrescine biosynthesis and of tumor promotion. Studies were made of its effect on induction of skin and bone tumors by repeated beta irradiation of the back of female ICR mice 3 times weekly at a dose of 3 Gy per exposure. When given at a concentration of 10 mg/ml in the drinking water, DFMO significantly delayed the time of tumor emergence and decreased the yield of skin tumors, although the cumulative tumor incidence computed by the Kaplan‐Meier method finally reached 100%. These results indicate that tumor‐promoting activity is involved in repeated beta irradiation, besides its tumor‐initiating activity.
Keywords: Radiation carcinogenesis, Repeated beta radiation, Inhibitor of tumor promotion, α‐Difluoromethylornithine, Mouse skin tumor
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