Carcinogenic Effect of in utero ^<252>Cf and ^<60>Co Irradiation in C57BL/6N×C3H/He F1 (B6C3F1) Mice

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C57BL/6N×C3H/He F1 mice were exposed in utero to 0, 1.0 and 2.7 Gy of ^<252>Cf or ^<60>Co at day 16.5th of gestation. Mice of both sexes were observed for 2 years. The females in the irradiated groups showed increases in the incidences of pituitary, mammary gland, liver and lung tumors. ^<252>Cf was more effective in inducing tumors than was ^<60>Co. Interestingly, the incidence of hematopoietic tumors decreased by irradia-tions with ^<252>Cf but not with ^<60>Co. The incidences of liver tumors in males increased by ^<252>Cf-irradiation, whereas, the incidences of skin and soft tissue tumors increased by ^<60>Co-irradiation. These results indicate that irradiation in utero during the late embryonic stage can induce tumors postnatally after a long latency. Moreover, females irradiated in utero had disfunction of the ovaries, evidence of impairment of the female's specific hormonal environment. This may be the cause of the low incidence of ovarian tumors and the high incidences of liver, lung and pituitary tumors in these female mice. Females with pituitary tumors had a high serum prolactin, which might be responsible for the concurrence of mammary gland tumors. These results indicate the importance of host factors in the development of radiation-induced tumors.
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