66 tients after radiation treatment for ankylosing spondylitis,!#9 etc.)}, and its etiological role was established without question bythe 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 amongthe general 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.15? On the basis of 2 cases per year per million people per rad amongthe exposed Japanese, the expectancy among the exposed Marshallese would bea total of about 0.33 cases. However, the normal incidence 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 spontaneouscases expected among the exposed Marshallese would be a total of 0.02 to 0.067. The ratio 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-vear period before the developmentof leukemiais of interest. The greater degree of hematologic depression in him thanin the other exposed boys indicates either 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 individually, were as 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 granulo- cytic form of leukemia, it is of interest that the near death. In spite of the long-term findings. morbid evidence of the disease was not apparent until the last few months. Oneyearbeforethe diagnosis of leukemia the peripheral blood cells appeared normal except for a possible increase in atypical monocytes. A preleukemic syndrome has been described for some cases of nonlymphocytic leukemias. '53,154 Linmanand Saarni!5state that the frequencv of the syndrome maybeas high as twocasesin five and that preleukemic findings ‘“‘reflect the early stage of myeloproliferative disorders which will eventually fulfil! the criteria to be classified as mvelomonocytic leukemias.’ The syndrome ts characterized by various findings, not all necessarily present,such as anemia with erythrocyte abnorma!ities, thrombocytopenia,atypical platelets in the pe- ripheral blood. and neutropenia.1!53.154 Chromosome abnormalities are reported in about half the cases.153 Isolated neutropenia is an occasional preleukemic finding; in the case reported here, the relative neutropeniais the only finding that might be considered as preleukemic. If the preleukemic phaseis considered to date back to near the time of radiation exposure in this case, then it had a longer course than is usually noted.154 The possibility that the granulocytic reserve was reduced in subject No. 54 as a result of radiation exposure was indicated by his granulocyte response being lower than that of his peers in response to challenge by childhood infections. One might speculate that the frequent infections to which the Marshallese are exposed may have plaved a role in accelerating the development of a radiauoninduced mutant leukemic clone. This would be similar in some ways to the role thought to be played by the thyroid-stimulating hormonein enhancing the development of tumors in radiationinjured thyroid glands, as has been seen in the Marshallese years after exposureof their thyroid glands to radioiodine from the fallout. The above findings do not rule out the possibility of a viral etiology for this leukemia. Because of the developmentofthis case of jeukemia, complete hematological examinations on the exposed Marshallese population are now being carried out semiannually instead of annually early bone marrow injury was characterized by having the greatest effect on the granulocytes, with B. OTHER MALIGNANCIES cytic system did not show evidenceoffailure until Malignancies other than thyroid cancer and leukemia (see Table 35) appeared to have a higher the thrombocytic and lymphocytic cells less affected and the erythrocyticcells least. The erythro-