orene) and any factor that causes hypothyroidismis ‘much higher.“ Radiation by either x-rays or I 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 cel] 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 his been so well studied after ultraviolet irradiation in bacteria.24 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 cell death may occur after division. It is likely that that the same process of division in cells carrying damaged DNA may be acritical factor in such stimulation. to Figure 3. Marked Growth Retardation and Hypothyroidisian ina Boy Exposed to Fallout al Eighteen’ Mouths of Lge. The taller boy standing beside him is his brother, wha ix a year younger. gulSde Neg 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 development of thyroid cancer.?3-4 In addition, the development of adenoniatous lesions of the gland in chil- DISCUSSION Adenomas and cancers of the thyroid gland can be produced in Jaboratory animals by a variety of agents 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 gland,'-"7 and irradiation of the gland with ['')'8-2e have all been shown to produce both benign and, malignant neoplasms. Furthermore, subtotal thyroidectomy in the rat has been reported to cause adehoma formation in the remaining thyroid tissue two years later???) All these procedures pothyroidism of varying degree, which effective stimulant to the secretion of pituitary gland. Under the influence Increased sensitivity of children's thyroid glands the development of neoplastic changes from produce hyserves as un TSH by the of TSH the thyroid gland first undergoes diffuse hyperplasia and hypertrophy and finally adenoma formation. In the cases of iodine deficiency and partial thyroidectomy, dren five to eleven years after treatment with ["! for thyrotoxicosis has been reported.2*" Doniach*! points out that cell division in the growing thyroid gland of the child may be a factor in this increased sensitivity to irradiation. On the average, 3 to 4 cell divisions are assumed to occur as the infant land rows from a size of about 1.5 gm. to a mature [7um. gland.? It thus seems reasonable to consider the enhanced tumorovenic effect of irradiation in) children to be due to the necessity for division of cells whose nuclei have previously been injured by raciation. The adult gland, on the other hand, would not be as prone to such radiation effects, since cell division is not believed to occur normally in the mature gland (mitotic figures are usually not discernible).272 Any factor, therefore, that causes increased secretion of TSH and thyroid hyperplasia will favor the development of neoplasia in a previously irradiated thyroid gland. Though the relation it is probable that no drug or carcinogenic agent is involved; also, the incidence of carcinomas after between adenomatous and malignant changes is not thyroid carcinoma after a combination of a carcinogenic agent (such as radiation or acetylaminoflu- The occurrence of adenomatoid nodules and 1 carcinoma of the gkand in the Marshallese who re- these treatments is relatively low. The incidence of clear it is apparent that the same situations predispose to the development of both types of chanze. . 901296 | PRIVACY ACT MATERIAL REMOVED. otrare oN TeTy lS ay A eT carcinogenesis although the mechanism is obscure. Obviously, any factor that stimulates the thyroid land to cause cell division will accelerate this process. Hypothyroidism produced by radiation damage to some of the thyroid cells will result in