and Nagasaki, the expected incidence among the Marshallese would have been about 0.83 cases. On the basis of Marshallese and USstatistics on spontaneous incidence, about 0.02 to 0.067 cases might have been expected. The ratio of incidence of radiation-induced to otherwise caused cases indicates that the Marshallese case was about 5 to 15 times more likely to have been radiation-induced than spontaneous. Although the latent period in this case was relatively ———- Mean counts of eight males exposed at <5 yr of age Gountsof this patient (No. 54)exposed at 1 yr of age ----— Counts of unexposed males of same age ” oO 4 “ 2 > 9 oO xc a long, the incidence In Japan (28 years after exposure) is still higher among E > - the exposed group than among the general population. Moreover, the in- cidence in Japan was higher among those exposed as children, particularly males, in whom the myelo- oy oO cytic form of the disease was more x 2 £ common. Q The greater effect of radiation ex- 2 5 posure on the myelocytes of this patient is interesting in view of the oD Zz later development of the myelocytic 4 6 F Rr . x oO 4 @2 Fy4\ a 27 a 5 \ 1f 0 L L | po 2 6 1 4 8 12 16 Months of Years —-—.—_____-__ This investigation was supported by the US Atomic Energy Commission. Edward S. Henderson, MD, James Mabry, MD, Time After Exposure Fig 2.—Comparison of blood cell counts of this patient, other exposed males, and unexposed males. centrations, Austraila antigen). Unromosomes studies of peripheral blood performed 12 years after exposure and of the bone marrow at the time of his present illness did not show aneuploidy or structural changes of the chromosomes. However, increased chromosome breakage (11% of the cells) that may have been related to radiation exposure or possibly to his disease was noted terminally. UnforJAMA, Jung30, 1975 9-Vo] 232, No 13 JUTS Io form of leukemia. Morphologic changes in the myelocytes were not apparent as late as one year before the development of the illness. The thrombocytic and erythrocytic elements did not show evidence of abnormality until near death. Neutrophilic depression was the only evidence of a possible preleukemic syndrome that has been described in some cases of this disease.‘ One might speculate in this case that the frequency of infections that occur in the Marshallese environment may have played a role in the developmentof a possible radiation-induced mutant clone. Joan Bull, MD, Maria Tomaszewski, MD, and Jacqueline Peng, MD, of the National Cancer In- stitute, and Gundabhaktha Chikkapa, MD, of tunately, bone marrow examinations were not done prior to his presentillness. Although the occurrence of one case of leukemia in this population is not statistically strong evidence of radiation as its cause, it must be seriously considered. With an incidence of two cases of leukemia per year per million people per rad, on the basis of Japanese statistics compiled at Hiroshima Brookhaven National Laboratory, assisted with this study. References 1. Conard RA, Dobyns BM, Sutow WW: Thyroid neoplasia as late effect of exposure to radioactive iodine in fallout. JAMA 214:316-324, 1972. 2, The Effects on Populations of Exposure to Low Levels of fonizing Radiation: Report of the Advisory Committee on the Biological Effects of Tonizing Radiations. National Academyof Science, National Research Council, November 1972. 3. Linman JW, Saarni MI: The preleukemic syndrome, Semin Hematol 11:73-92, 1974. Acute Myelogenous Leukemia—Conard rnointed ano ruonsned in tne United States of America 1357