Risk of cancer among children exposed in utero to A-bomb radiations, 1950-84.

This study examines the risk of cancer (incidence) over 40 years among the in-utero exposed survivors of the atomic bombing of Hiroshima and Nagasaki, and adds eight years of follow-up to a previous report confined to mortality. Only two cases of childhood cancer were observed among these survivors in the first 14 years of life; both had been heavily exposed. Subsequent cancers have all been of the adult type. Not only did the observed cancers occur earlier in the 0.30 + Gy dose group than in the 0 Gy dose group but also the incidence continues to increase, and the crude cumulative incidence rate, 40 years after the A-bombing, is 3.9-fold greater in the 0.30 + Gy group. In the observation period 1950-84, based on the absorbed dose to the mother's uterus as estimated by the 1986 dosimetry system (DS86), the relative risk of cancer at 1 Gy is 3.77 with a 95% confidence interval of 1.14-13.48. For the entire 0.01 + Gy dose group the average excess risk per 10(4) person-year-gray is 6.57 (0.07-14.49) and the estimated attributable risk is 40.9% (2.9-90.2%). These results, when viewed in the perspective of fetus doses, suggest that susceptibility to radiation-induced cancers is higher in prenatally than in postnatally exposed survivors (at least those exposed as adults). However, definitive conclusions must await further follow-up studies.