C FICIAL USE ONLY ANNEX - REPORT OF SOME RECENT OBSERVATIONS OF THE ATOMIC BOMB CASUALTY COMMISSION Seymour Jablon The core of the ABCC research program consists of the Life Span Study which traces the mortality of a cohort of about 109,000 Japanese of Hiroshima and Nagasaki including survivors who were located near and at varying distances from the hypocenters. The controls consist of persons who immigrated into the cities after the bursts or were in the city beyond range of the weapon effects. Additional control mortality information is obtained from entry into the conventional Japanese National Vital Statistics reporting system with the assistance of the Japanese National Institute of Health. The population comprising the Life Span Study is a "floating" cohort as the youngest members are 26 years old; epidemiological treatment. this age structure occasions unusual The Life Span Study is backed up by two major programs which are equally critical to the overall mission of ABCC. They are: 1) The Autopsy Pathology Studies program which has obtained autopsies on 40% of deceased members of the Life Span Study. In view of the Japanese custom of cremation or other disposal within 24 hours of death, the program has been phenomenally successful; 2) The Adult Health Study conducts biennial physical examinations on a sub-cohort of 20,000 persons drawn from the larger Life Span Study cohort. Its procedures supply information on the biomedical and epidemiologic changes occurring as the exposed population ages. It has the added value of diagnosing the onset of possibly lethal disease in time to institute proper medical care. A new analysis of mortality through 1970 in the Life Span Study has recently been completed, and highlights from this were presented. Analyses— were made with reference to the so-called T-65 radiation dose estimates, the dosimetry system devised by John Auxier and staff of the Health Physics Division of the Oak Ridge National Laboratory. 1, The mortality ratios (ratio of actual number of deaths to the number expected from Japanese national death rates) from all diseases were very high for survivors whose doses were estimated to exceed 200 rads and who were children under 10 at the time of the bombings (ATB). The mortality ratios declined with increasing age at time of exposure, but were slightly elevated even among those aged 50 or more ATB. 2. Mortality from leukemia among the survivors has been declining since 1950-54, but was still more than 15 gimes expectation in 1965-70 among high dose survivors (200 + rads). 3, In terms of age ATB, sensitivity to radiation leukemogenesis was greatest among children under 10 years of age, least among those 10 to 19, and then rose with increasing age. OFFICIAL USE ONLY