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-
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