Acute Radiation Exposure and Risk of Second Primary Cancers in Atomic Bomb Survivors

Abstract

ISEE-0254 Background and Objective: Studies of the Japanese Atomic Bomb Survivors provide some of the most comprehensive evidence to date of the impact of ionizing radiation exposure on cancer risk. Radiation-associated risks for first primary cancers have been characterized extensively in A-bomb survivors, and this research has guided risk assessment for radiation exposure in environmental, occupational, and medical settings. Since comparatively little is known about the risk of subsequent primary cancers, we investigated the risk of second primary solid cancer and leukemia among survivors of a first primary cancer in the Life Span Study of Atomic Bomb Survivors. Methods: Second primary cancer incidence data for 1958-2001 was provided by the Hiroshima and Nagasaki population-based cancer registries. Poisson regression analysis was used to examine risks of second primary cancer, among survivors of a first cancer, in relation to radiation dose to the colon (γ-ray dose plus 10 times the neutron dose, estimated from the DS02 dosimetry system). Results: Of 13786 A-Bomb survivors with a first primary cancer, 1331 developed second solid cancers, and 33 developed leukemia. Compared to survivors with radiation dose <0.005 gray (Gy), survivors exposed to ≥2.00 Gy were at significantly elevated risk of developing second primary solid cancers (RR = 2.3; 95% CI: 1.7, 3.1) and second primary leukemia (RR = 7.8; 95% CI: 2.2-28.0) in analyses adjusted for sex, city, exposure age, attained age, and age at first diagnosis. For linear dose response models, the excess RRs/Gy were 0.5 (95% CI: 0.3, 0.7) and 3.2 (95%CI: 1.0, 8.3) for second primary solid cancers and leukemia, respectively. Conclusion: While further research is necessary, we observed significantly elevated risks of second primary cancers associated with exposure to ionizing radiation in Atomic Bomb Survivors with a first primary cancer, providing further evidence of the long-term risks associated with exposure.