at ke ' . ae ahh ,# al : thay, at Aa AT Pee Boe, @ ‘ C@ Radiation-Associated Thyroid Carcinoma 249 of progression of the disease. Three of the cases of thyroid cancer were in the Utirik group, two occurring in the past year. Though highly significant statistically, this is a puzzling development, since the number of benign tumors does not appear to be increased in this group, with none appearing in the high risk group of 58 children aged < 10 at exposure. One of 4 Rongelap children exposed in utero, exposed at the end of the second trimester, (175 rads of gamma radiation and an unknown amount of radioiodine from the mother), developed benign thyroid nodules 20 years after exposure. Though a number of cases of myxedema have been reported in babies born of mothers treated with radioiodine, this is thought to be the first case of nodularity reported. Fig. 2 shows that at 22 weeks the thyroid is actively functioning in the fetus, though it is not possible to calculate the dose to the gland of this particular boy. It is noteworthy that his mother had a thyroid cancer removed during the past 6 months. The boy has not shown any other effects of his in utero exposure. The other 3 subjects exposed in utero have appeared to be normal. LATENT PERIOD Fig. 3, a plot of the time of development of thyroid tumors vs dose, indicates that thyroids that received lower doses developed tumors later than those receiving higher doses. This effect on latent period seems to be roughly dose dependent. Other studies of radiation induced cancers in people exposed as children have not demonstrated clear-cut correlation between radiation and length of latent period (11). However, most of these studies suffer from uncertainty of exact dosage and insufficient spread of doses and of times when thyroid tumors actually developed. Some degree of dependence of latent period on dose seems reasonable, Since a higher dose causes greater cell destruction resulting in greater thyroid hypofunction and thyroid stimulating hormone (TSH), which is thought to be an important factor in neoplasia induction, as discussed earlier by Dr. Doniach. With lower doses more cells |