Incidence of leukemia in survivors of the atomic bomb in Hiroshima and Nagasaki, Japan

Data have been presented concerning the incidence and death rate from leukemia for the years 1948, 1949 and 1950 in the populations of Hiroshima and Nagasaki, Japan, which were exposed to radiation effects of the atomic bombs exploded in 1945. The incidence and death rate from leukemia has been compared in the exposed and non-exposed populations of Hiroshima and Nagasaki and also within the exposed population by distance from the hypocenter. The data show an increase in the incidence of leukemia in the total exposed populations compared with the total non-exposed populations of the two cities. A highly significant increased incidence of leukemia is found in the subjects exposed to the radiation at distances of less than 2,000 meters as compared with those exposed beyond 2,000 meters. Analysis of medical radiation histories in exposed subjects with leukemia presents evidence of severe radiation injury in a high proportion of the cases exposed under 2,000 meters. There is little evidence, by this same analysis, of severe radiation injury occurring beyond 2,000 meters. The same pattern of findings of the collective analysis is present in the data obtained separately in Hiroshima and Nagasaki. Leukemia in the cases exposed both under 2,000 meters and over 2,000 meters occurs most frequently in the early and intermediate age groups. Acute leukemia and myelocytic leukemia have predominated in all cases irrespective of the individual's distance from the hypocenter at the time of the bomb explosion. Chronic lymphatic leukemia was observed in only a single case. The number of cases is small and the types of leukemia observed are not inconsistent with the age distribution in which they occurred. Comparative differences in the sex distribution in the cases of leukemia are slight and the total numbers too small to warrant any conclusions.