PRIVACY ACT MATERIAL REMOVED orene) and ans factor that causes hypothyroidism is much higher.* Radiation by either x-rays or 143! is particularly effective since it simultaneously acts as a carcinogen and, by impairing the functional capacity of the gland, also induces TSH secretion and thyroid stimulation. Several aspects of radiation damage may be considered. Cytoplasmic damage may result in enough functional damage to result in cell death, or repair may occur if the damage is not too extensive. Injury to nuclear material may result in death of the cell if enough deoxynucleic acid (DNA) is altered so that the process of its transformation for synthesis of protein is seriously inhibited. Restoration of DNA may occur after these damaging effects, as has been so well studied after ultraviolet irradiation in bacte- ria2* On the other hand, DNA that is not restored, may not affect cell function if that portion of the DNA is repressed and not undergoing transformation, but cel] death may occur after division. It is likely that that the same process of division in cells carving damaged DNA maybe acritical factor in carcinogenesis although the mechanism is obscure. Obviously, any factor that stimulates the thyroid gland to cause cell division will accelerate this process. Hypothyroidism produced by radiation damage to some of the thyroid cells will result in such stimulation. Increased sensitivity of children’s thyroid glands Fiat ke 3. Marked Growth Retardation and Hypotlarodinm ita Boy Exposed to Fallout at Erghteen Months of tee. The taller bay standing beside hanes hes brother. who ww a year \ounger, DISCUSSION Adenomas and cancers of the thyroid gland can be produced in laboratory animals by a variety of avents or regimens that interfere with the ability of the gland to synthesize thyroid hormone. Iodine deficiency,® agents that chemically inhibit thyroxine synthesis such as thiouracil,""“ x-irradiation of the dand,3"7 and irradiation of the ghand with [#1,!8-2° have all been shown to produce both benign and malignant neoplasms. Furthermore, subtotal thyroidectoms in the rat has been reported to cause adenoma formation in the remaining thyroid tissue two years dater2!#? All these procedures produce hy- to the development of neoplastic changes from radiation exposure has been amply demonstrated. A series of retrospective and prospective studies have clearly shown the causal relation of irradiation of the thymic region in infants and the later develop- ment of thyroid cancer.25?8 In addition, the development of adenomatous lesions of the gland in chil- dren five to eleven veurs after treatment with [" for thyrotoxicosis has been reported." Doniach®! points out that cell division in the growing thyroid «land of the child may be a factor in this increased sensitivity toirradiation. On the average, 3 to 4 cell divisions are assumed to occur as the infant gland grows from a size of about 1.5 gm. to a mature 17em. gland.? It thus seems reasonable to consider the enhanced tumorogenic effect of irradiation in chil- dren to be due to the necessity for division of cells whose nuclei have previously been injured by radiation. The adult wland, on the other hand, would not be us prone to such radiation effects, since cell pothyroidism of varving degree, which serves as an division is pituitary gland. Under the influence of TSH the thyroid gland first undergoes diffuse hyperplasia and cernible).272 Any factor, therefore, that causes increased secretion of TSH and thyroid hyperplasia will favor the development of neoplasia in a pre- effective stimulant to the secretion of TSH by the hypertrophy and finally adenoma formation. In the cases of iodine deficiency and partial thyroidectomy, it is probable that no drug or carcinogenic agent is involved; also, the incidence of carcinomas after these treatments is relatively low. The incidence of thyroid carcinoma after a combination of a carcinogenic agent (such as radiation or acetvlaminoflu- not believed to occur normally in the mature gland (nitotic figures are usually not. dis- viously irradiated thyroid glind. Though the relation between adenomatous and malignant changes is not clear it is apparent that the same situations predis- pose to the development of both types of change. The occurrence of adenomatoid nodules and 1 earcinamia of the gland in the Marshallese who re- MOVED PRIVACY ACT MATERIAL RE