66
tients after radiation treatment for ankylosing
spondylitis,149 etc.), and its etiological role was
established without question by the high incidence
of leukemia in the Japanese exposed to the atom
bomb.150.151
Somefindings in the Japanese tend to support
radiation etiology in this Marshallese boy. In his
case the latent period was quite long, but the incidence of leukemia in Japan is still (after >25
years) higher among the exposed group than
amongthegeneral population. Also, the incidence
has been higher among those exposed in childhood, particularly males, in whom the granulocytic
form of leukemia has been prevalent; and the same
form has been more prevalent in cases with longer
latent periods and lower exposures.!52 On the
basis of 2 cases per year per million people per
rad amongthe exposed Japanese, the expectancy
amongthe exposed Marshallese would bea total
of about 0.33 cases. However, the normalincidence
of leukemia in the Marshallese, from the sketchy
statistics available, appears to be low, about 20
cases per year per million compared with 60 to 70
in the U.S.; thus the numberof spontaneous cases
expected amongthe exposed Marshallese would
be a total of 0.02 to 0.067. Theratio of radiationinduced to spontaneous expectancy (0.33:0.02 or
0.33:0.067) indicates that chances are about 5 to
15 times as great that this Marshallese case was
radiation-inducedas that it was spontaneous.
Review of the hematological data on subject
No. 54 over the 18-year period before the developmentof leukemiais of interest. The greater degree
of hematologic depression in him than in the other
exposed boysindicateseither a greater radiation
dose to the hematopoietic tissues or greater sensitivity or proclivity to marrow depression. (None
of the peripheral granulocyte levels in the other
boys, exposed or unexposed, plotted individyally,
wereas low as his.) Perhaps his radiation dose was
actually greater, since he was the youngest Rongelap child exposed and maytherefore have been
in closer contact with the fallout source on the
ground. Being younger mightalso imply greater
radiosensitivity.
In view of the later developmentof the granulocytic form of leukemia, it is of interest that the
early bone marrow injury was characterized by
havingthe greatest effect on the granulocytes, with
the thrombocytic and lymphocytic cells less affected and the erythrocytic cells least. The erythro-
cytic system did not show evidenceoffailure until
near death. In spite of the long-term findings,
morbid evidenceof the disease was not apparent
until the last few months. Oneyearbefore the diagnosis of leukemia the peripheral blood cells appeared normal except for a possible increase in
atypical monocytes.
A preleukemic syndromehas been described for
some cases of nonlymphocytic leukemias. 153.154
Linmanand Saarni!54 state that the frequency of
the syndrome may beashigh as twocasesin five
and that preleukemic findings “reflect the early
stage of myeloproliferative disorders which will
eventually fulfill the criteria to be classified as myelomonocytic leukemias.”’ The syndromeis char-
acterized by various findings, notall necessarily
present, such as anemia with erythrocyte abnormalities, thrombocytopenia,atypicalplatelets in the peripheral blood, and neutropenia.453.154 Chromosome abnormalities are reported in about half the
cases.153 Isolated neutropeniais an occasional!preleukemic finding; in the case reported here, the
relative neutropenia is the only finding that might
be considered as preleukemic. If the preleukeinic
phase is considered to date back to near the time
of radiation exposurein this case, then it had a
longer course than is usually noted.!54
The possibility that the granulocytic reserve was
reduced in subject No. 54 as a result of radiation
exposure was indicated byhis granulocyte response
being lower than thatof his peers in response to
challenge by childhood infections. One mightspeculate that the frequent infections to which the
Marshallese are exposed may have plaved a role
in accelerating the development of a radiationinduced mutant leukemic clone. This would be
similar in some ways to the role thought to he
played by the thyroid-stimulating hormone in enhancing the development of tumorsin radiation-
injured thyroid glands, as has been seen in the
Marshallese years after exposure of their thyroid
glands to radioiodinefrom the fallout. The above
findings do not rule out the possibility of a viral
etiology for this leukemia.
Because of the developmentofthis case of leukemia, complete hematological examinations on
the exposed Marshallese population are now being
carried out semiannually instead of annually.
B. OTHER MALIGNANCIES
Malignancies other than thyroid cancer and
leukemia (see Table 35) appeared to have a higher