Risk of cancer among children exposed to atomic bomb radiation in utero: a review.

We have examined the risk for cancer (incidence) over a period of 40 years, 1945-1984, among 1829 persons exposed in utero to the atomic bombing of Hiroshima and Nagasaki. This report adds eight years of follow-up to a previous report which was 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 these latter cancers occur earlier in persons exposed to greater than 0.30 Gy than in unexposed (0 Gy) but the incidence continues to increase, and the crude cumulative incidence rate 40 years after the bombing is 3.9-fold greater in persons exposed to greater than 0.30 Gy. In the observation period 1950-1984, the relative risk for cancer at 1 Gy, based on the absorbed dose to the mother's uterus as estimated by the Dosimetry System 1986 (DS86), is 3.77 with a 95% confidence interval of 1.14-13.48. For all persons exposed to greater than 0.01 Gy, the average excess risk per 10(4) person-year-Gy 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 fetal doses, suggest that susceptibility to radiation-induced cancers is higher in survivors exposed prenatally than in those exposed postnatally (at least, those exposed as adults). However, definitive conclusions must await further follow-up studies.