CANCER MORTALITY AMONG ATOMIC-BOMB SURVIVORS EXPOSED IN-UTERO OR AS YOUNG-CHILDREN, OCTOBER 1950 MAY 1992

Cancer mortality for the period from October 1950 through May 1992 was analyzed in atomic bomb survivors exposed in utero. Risk estimates fo r this group were also compared to those for survivors who were less t han 6 years old at the time of exposure. The cohorts studied include 8 07 in utero survivors and 5,545 persons exposed during childhood with all members of both groups having estimated doses of at least 0.01 Sv. The comparison group includes 10,453 persons with little (< 0.01 Sv) or no exposure. Analyses were limited mainly to cancer deaths occurrin g between the ages of 17 and 46. Only 10 cancer deaths were observed a mong persons exposed in utero. However, there is a significant dose re sponse with an estimate of excess relative risk per sievert (ERR/Sv) o f 2.1 (90% confidence interval of 0.2 to 6.0). This estimate does not differ significantly from that for survivors exposed during the first 5 years of life. The cancer deaths among those exposed in utero involv ed leukemia (2), female-specific organs (3) and digestive organs (5). Nine deaths occurred in females, where the excess risk for all solid c ancers has a 90% confidence interval on the ERR/Sv of 1.6 to 17. Signi ficant risks were found for cancers of the digestive system [90% confi dence interval (CI) on the ERR/Sv of 0.7 to 20] and for female-specifi c cancers (90% CI on the ERR/SV of 0.7 to 42). These risks do not diff er significantly from those seen in females exposed as children. There were no deaths from solid cancer in men exposed in utero. The ERR/Sv has an upper 95% confidence bound of 2.5 which does not differ from th at for exposed children, where the upper 95% confidence bound is 1.5. The sexes differ even when female-specific cancers are excluded from t he comparison. Although there were only two leukemia deaths among thos e exposed in utero, the leukemia death rate for this group is higher t han that in the comparison group (P = 0.054) with an exposure effect t hat is about half the magnitude and not significantly different from t hat seen after childhood exposure (P = 0.103). However, there is no ev idence of a dose response among those exposed in utero because no high -dose leukemia deaths were observed, a result that differs considerabl y from that for those exposed as children. There is a need for caution in the interpretation of these data. First, the number of cancer deat hs is small; second, there is unexplained significant difference in th e mortality from solid cancer between the sexes; and third, the excess of leukemia in those exposed in utero is not reflected in an increasi ng dose response. (C) 1997 by Radiation Research Society.