€ 252 Radiation-Associated Thyroid Carcinoma COMMENTS AND CONCLUSIONS € f From the Marshallese experience it appears that the greater propensity for the development of thyroid nodularities after radioiodine exposure in the children than in the adults is related not only to the smaller size of their glands (resulting in larger doses) but possibly also to the rapid growth of the gland from 1-2 grams at birth to 18 at maturity. Other factors such as the stress of puberty and frequency of pregnancy May also have played a role. The lower incidence of thyroid cancer in the Rongelapese exposed as children, as adults, than in those exposed is worthy of comment. One can postulate that the thyroid doses in the Rongelap children (7001400 rads) were high enough to cause many cells to die at mitosis because of lethal damage to the reproductive mechanism and thus to reduce the number of cells at risk for malignant transformation. At lower doses, as in the adult group, a greater number of cells would be spared for malignant transformation. One would have to assume that in the children's thyroids the high dose effect overrode the possible enhancing effect of the growth factor for cancer induction. The high incidence of benign thyroid tumors in the children could be due to the increased cell destruction with greater hypofunction and increased TSH stimulation of the remaining cells producing many small nodules. With doses ina still higher range (> 2000 rads?) one might expect such extensive cell destruction to result in hypothyroidism and, because of the fewer surviving cells at risk, few- er tumors. This is the situation in patients developing hypothyroidism years after radioiodine treatment for Graves' disease. Perhaps the two Marshallese boys who developed myxedema without thyroid nodules received doses in this higher range. It is quite likely that the final tally of thyroid tumors in the Marshallese is incomplete at this time Since new lesions are still occurring. The mean latent period for radiation-induced thyroid tumors may be as long as 30 years (11). Furthermore, on the basis of