Carcinogenic effect of in utero 252Cf and 60Co irradiation in C57BL/6N x C3H/He F1 (B6C3F1) mice.

C57BL/6N x C3H/He F1 mice were exposed in utero to 0, 1.0 and 2.7 Gy of 252Cf or 60Co 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. 252Cf was more effective in inducing tumors than was 60Co. Interestingly, the incidence of hematopoietic tumors decreased by irradiations with 252Cf but not with 60Co. The incidences of liver tumors in males increased by 252Cf-irradiation, whereas, the incidences of skin and soft tissue tumors increased by 60Co-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.