The effect of age at exposure to a sublethal dose of fast neutrons on tumorigenesis in the male rat.

Male rats were irradiated with a single whole-body sublethal dose (215 to 230 rads) of fast neutrons as juveniles (1 month), young adults (3 months), or old adults (21 months of age) and maintained in a duration-of-life study. The extent of tumorigenesis was analyzed with respect to the general types of tumors, the percentage of animals with tumors, and the distribution of tumors among organs within each age group. In no instance did irradiation result in a significant excess of animals with tumors in the oldest group. Radiation was particularly effective in inducing benign epithelial and nonepithelial tumors as well as malignant nonepithelial tumors in the juvenile group and malignant epithelial tumors in the young adult group. The skin, kidneys, and Langerhans's islands