Special susceptibility of the child to certain radiation-induced cancers.

The carcinogenic effects of exposure to ionizing radiation vary markedly with age, as revealed by studies of Japanese atomic bomb survivors and of Marshall Islanders exposed to fallout from U.S. nuclear weapons tests in the South Pacific in 1954. An increase in cancers of adulthood after intrauterine exposure, as reported in 1988, has not been sustained. After childhood exposure, increases in leukemia, breast cancer, and thyroid cancer are well established. The carcinogenic effects of radiation on the young have been reported after intrauterine exposures and after exposures during childhood. Cancers with short latent periods such as leukemia occur during childhood, but those with long latent periods such as breast cancer occur in adulthood.