Age dependence of radiation-induced liver tumor of mice

Background:Because of the increased occasion of medical exposure of radiation to children, effects of radiation on them are of great concern in recent years. One of the most significant concern is cancer development, which results in an effect of increase in age-specific mortality and the shortening of life expectancy. However, available information on the childhood exposure is quite limited. Using animal models, we clarified the dependence of radiation-induced liver cancer on the age at exposure. \nMaterials and Methods:In order to estimate age dependence of susceptibility to radiation carcinogenesis, fifty male and female B6C3F1 mice per group were exposed to gamma-rays (137Cs) at the dose of 2.0 or 4.0 Gy at fetus (17 days post-conception, 17 dpc), neonate (1 week after birth) and adult (7 weeks after birth). All mice were allowed to live throughout their entire life spans. Liver tumors as well as tumors from other organs were analyzed histologically to determine tumor incidence and tumor spectrum at death. \nResults and Discussion:Multiple types of liver tumors such as hepatoblastoma, hepatocellular adenoma, hepatocellular carcinoma, histiocytic sarcinoma and hemangioma were observed from mice after exposure to 2.0 or 4.0 Gy of gamma-rays, we focused on hepatocellular carcinoma (HCC). We found that mice of the neonatal age were most susceptible to radiation-induction of HCC; the tumor incidence in male mice that were exposed to 2.0 or 4.0 Gy increased up to 50%, while that in unirradiated mice was 24%. However, the HCC incidence of fetal and adult exposure groups was not influenced by irradiation, being only 20~30%. In female, neonatal mice exposed to 4.0 Gy showed 25% of HCC incidence, while the unirradiated mice did not develop HCC at all. The age dependence of radiation-induction of tumors other than liver tumors will be also described. Significant life span shortening was the most evident after neonatal irradiation in both male and female mice. In summary, mice in the neonatal period were the most susceptible to radiation induction of HCC and life-span shortening.The 3rd JCA-AACR Special Joint Conferenc