Radiation-induced Thyroid Cancer—What's New?

Several years ago I wrote that there was little more to be learned about radiation-induced thyroid cancer ( 1 ) . I was mistaken. After 50 years of research, it was known that the thyroid gland of children, but not adults, was especially sensitive to the carcinogenic action of ionizing radiation, that a straight line adequately represented the relationship between dose of radiation and effect, that effects for thyroid cancer were seen at lower dose levels (on the order of 0.10 Gy) than those observed for most other radiation-induced cancers, that very high dose levels resulted in a lowering of risk because of cell killing, that screening had a profound influence, and that mixtures of radioiodines could cause thyroid cancer. However, the carcinogenic effect of 131 I exposure of children was uncertain. The article by Cardis et al. ( 2 ) in this issue of the Journal has provided new and, if confirmed, provocative information on the risk of radiation-induced thyroid cancer and on the modifying role of diets deficient in stable iodine and of administering iodine supplements months after the exposure has occurred.