RADIOAC PIVE PALTOU P-CONARD EL PBa7 OAL. arene) and ans factor that causes hypothyroidism is minch higher2* Radiation by cither x-rays or [is particularly effective since it simultaneously acts as a carcinogen andl, by impairing the functional capacity of the gland also induces TSH secretion and thyroid) stimulation. Several aspects of radiation danwige mas be con- sidered. Cytoplasmic damage may result ta enouch finetional damage to result in cell death, or repatr mas occur if the damage is not too extensive. Inpurs to nuclear material may result in death of the cell if cnoaugh deoxviucleic acid) GONA) is altered so that the Process of its transformation for syuthesis at protein is seriously inhibited. Restoration of DNA May occur after these damaging effects, as has been so well studied after ultraviolet irradiation in bacteria! On the other hand, DNA that is not restored, may not affect cell function if that portion of the IDNA is repressed and not undergoing transformu- tion, but cell death may occur after division. It is likely that that the same process of division in cells carrving damaged DNA may be a critical factor in carcinogenesis although the mechanism is obscure. Obviously, ans factor that stimulates the thyroid land to cause cell division will accelerate this PYOCeSsS. Hypothyroidism produced by raciation damage to some of the thyroid cells will result in such stimulation. Increased sensitivity of children’s thyroid) glands to Houre Sb. Meaked Growth Retardation ane Hypothyroutim ina Boy Exposed ta Fallout at frgdteen: Maths af Ave. The tatles hay standing beside ham os hes brother, whew aver JOHHEE DISCUSSION Adcnomas and cancers of the thyroid gland can be produced in laboratory animals by a variety of dents or regimens that interfere with the ability of the gland to svathesize thyroid hormone. lodine deficiency," agents that chemically tnhibit dhyroxine wnthesis such as thiouracil,!’ ™ x-irradiation of the dand, "7 and irradiation of the gland with [',!=2 have all been shown to produce both benign and Malignant neoplasms. Furthermore, subtotal thy roidude an Part rape [vaiph -roum. per esponse to tof grow [l be dis dectomy in the rat has been reported to cause ade- “oma formation in the remaining thyroid tissue two ‘ears Jater.21? All these procedures produce hyMthyvroidism of varving deuree, which serves as an ‘fective stimulant to the secretion of TSH by the Mtuitary ghind. Under the influence of TSH the ‘hyroid gland first undergoes diffuse hyperplasia ane pertrophy and finally adenoma formation. In the “ses of iodine deficiency and partial thyroidectomy, is probable that no drug or carcinovenic agent is ‘volved: also, the incidence of Curc i nonnits iter ided to im hese treatments. is relatively low. The incidence of the more Ryroid carcinoma after a combination of a carcinoin Septenr tnic avent (sach as radiation or acets laminoffu- the development of neoplastic changes from radiation exposure has been amply demonstrated, series of retrospective and prospective studies have clearly shown the causal relation of irradiation of the thyinic region in infants and the later development of thyroid cancer2>?* In addition, the develop- ment of adenomatous lesions of the gland in) chil- dren five to eleven vears after treatment with I'*! for thyrotoxicosis has been reported" Doniach®! points out that cell division in the growing thyroid gland of the child may be a factor in this increased seusitivity to irradiation. On the average, 3 to 4 cell divisions are assumed to occur as the infant gland erows froin a size of about 1.5 gm. to a mature 17gm. “haind.? It thus seems reasonable to consider the enhanced tumorogenic effect of irradiation in chil- dren to be duc to the necessity for division of cells whose nuclet have previously been injured by radi- ation. The adult gland, on the other han, would hot be as prone to such radiation effects, since cell division is not believed to occur normally in’ the mature land (mitotic figures are usually not. discernible)2742 Any factor, therefore, that causes in- creased secretion of TSH and thyroid hyperplasia will favor the development of neoplasia in a previously irradiated thyroid gland. Though the relation between adenomatous and malignant chanwes is not clear it is apparent that the same situations precis- pose to the development of both types of change. The occurrence of adenomatoid nodules and 1 carcinoma of the ehand in the Marshallese who re- BEST AVAILABLE COPY