Does radiation cause liver cancer Comparison of radiation effects in atomic bomb survivors and other populations

摘要

Recent studies of atomic bomb survivors have shown that risks of liver cancer are significantly increased by radiation exposure. This contrasts with mortality studies of other radiation-exposed populations, which generally have not shown a significant radiation effect for this cancer. Because the liver is a frequent site to which other tumors metastasize, liver cancer is one of the most difficult cancers to correctly diagnose. Studies of liver cancer in A-bomb survivors and other populations have documented high percentages of tumors metastasized to the liver being incorrectly diagnosed as liver tumors. In addition, many deaths due to liver cancer have been incorrectly attributed to cirrhosis or chronic hepatitis. Studies of incident or pathology-confirmed liver cancer cases in A-bomb survivors have found higher radiation risk estimates for liver cancer than mortality studies in this cohort. Most studies of radiation and liver cancer in other radiation-exposed cohorts have been mortality studies, and thus,would include many misclassified liver cancers. Liver cancer was consistently associated with radiation exposure in studies of four cohorts exposed to Thorotrast, a previously used radiology contrast agent. However, the histologic subtypes of liver cancer and type of radiation exposure (external rather than internal) differ from those experienced by the A-bomb survivors. Liver cancer in atomic bomb survivors is primarily hepatocellular carcinoma (HCC), rather than the cholangiocarcinoma and hemangiosarcoma subtypes more associated with Thorotrast exposure A recent case control study of the joint effects of radiation and viral hepatitis in the etiology of HCC, showed that A-bomb radiation had a significantly stronger effect among subjects who were infected with the hepatitis C virus (HCV). No significant interaction between hepatitis B viral infections and radiation in the etiology of this disease was found. We compared incidence and mortality studies of liver cancer conducted in a wide variety ofradiation-exposed populations, in terms of their radiation risk estimates for liver cancer, the background level of liver cancer in the cohort, HCV prevalence in the population from which the cohort was drawn, and other factors. The differences between the radiation risk estimates for atomic bomb survivors and other cohorts may reflect liver cancer diagnosis errors. Varying risk estimates may also reflect differences in the prevalence of HCV in radiation-exposed cohorts,