a LATE EFFECTS OF RADIOACTIVE IODINE IN FALLOUT development of thyroid carcinoma has been shown experimentally in rats (30). The one carcinoma in the Marshallese adult is quite different from the type of disease about which we have thus far been concerned, since there was no hyperplasia 1239 plasms in a significant number of exposed individuals. It would also seem likely that lesser amounts of radiation, every direct hit on a gene beingeffective, might also lead to cancer formation. This, however, be- comes a problem in disease statistics and is one that is currently engaging the inter- of the surrounding thyroid gland. This was est of many, thus far with no clear-cut answers, The experience in the Marshall population. On the other hand, there is one portion of the spectrum of thyroid radiation effects in man. typical, then, of the usual case of thyroid carcinoma occurring in a nomirradiated considerable evidence that thyroid carctnoma in young adults, and especially in children, is frequently caused by radiation of the cervical area in childhood. Lindsay and Chaikoff (20) have reviewed the various clinical reports on this subject, and Winship and Rosvoll (31) reported that as many as 80% of children with thyroid car- cinoma, in a series of 562 -cases, have a history of prior cervical irradiation, The amount of radiation, which 1s usually given in the form of X-ray therapy for thymic hypertrophy or tonsillitis, can be even smaller than that in the Marshallese population, being in the range of 90 to 1,500 rads. This was the dose range in a prospec: tive study of over 4,500 patients in whom thyroid carcinoma developed, on the av- erage, 1] years later in approximately 0.5% of persons exposed to such radiation (24, 32, 33). Although adults may not be immune to radiation-induced tumors——as sug- gested by the apparent increased preva- Islands has, at least, served to illuminate I would now like to call for questions. Dr. WoLtFF: What fraction of the radia- tion was from 1]? Dr. Conarn: Probably less than half. Dr. WotrF: In connection with that, was there any 17°I? Have you gotten any counts on the material that was removed surgically? Dr. RALL: °I has a half-life of approximately 17 million years, so that essentially it is unradioactive. For any such molecules in the lifetime we are talking about, they do not decay but are still there to be measured by neutron activation. The question is, would there be any there? Well. we do not know. Maybe we should have mea- sured it. Maybe there is still tissue left. I am afraid that 10 years of biological turnover in the affected individuals would leave almost none of the origtnal iodine around for measurement. Dr. JESSE RoTH: With hyperthyroid pa- sumably require cell diviston for their expression. It appears clear that the sizable amounts of irradiation that we have been discussing about 10,000 rads, and these children got have the potential to produce thyroid neo- the early uptake of iodineis high, but then a large portion of this todine is not organi- e tients who have been treated with radioiodine it is common to see a defect where There is a difference in the radiation delivered: The hyperthyroid patients get EO lence of thyroid cancer in adults exposed to the atomic bomb in Hiroshima (34) and other types of radiation (35, 36)—the propensity for this sequela in children is almost surely related to the fact that in the celis of the growing thyroid gland there must be numerous mitoses, whereas mitoses in the adult gland are rare. The gene al- terations leading to cancer formation pre- oe eeee of such TSH suppression to prevent the | e ee June 1967 fied. I was curious as to why it did not seem to show up in these radiated groups. Dr. Rossins: I have no real answer. about 1,000 rads. Also, these were children who did not have so much damage that they could not grow nodular goiters. The hyperthyroid patients are probably dam- —itae, re Volume 66, No. 6