Cancer Risk In Czech Uranium Miners

National Institute Of Environmental Health Sciences

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Abstract

We have been studying cancer incidence in a cohort of 16,434 underground uranium miners from the Czech Republic. Eligible miners worked at least one year underground prior to January 1, 1976, and were alive and living in the Czech Republic on January 1, 1977. The cohort was followed for cancer incidence and mortality through December 31, 1992 by linking with the Czech cancer registry. Detailed records on daily work location and radon levels, smoking, dusts, and gamma radiation were obtained for a 2,000-person stratified random sample of the cohort and all cancer cases for use in case-cohort analyses. Cancer follow-up was extended through 1998 to increase the number of miners with cancers of sites other than the lung for inclusion in case-cohort analyses. Lung cancer was diagnosed in 752 miners through 1992. Fifty-six percent of miners began mining after 1960 when industrial hygiene measures substantially reduced radon exposure. Cumulative exposure was less than 50 WLM for 72% of the cohort. Cancer of sites other than the lung was diagnosed in 1100 miners. We previously reported results from a case-cohort analysis of risk for hematopoietic cancers, reporting that radon and gamma irradiation appeared to be independent risk factors for hematopoietic cancers in general and leukemia specifically. Although chronic lymphocytic leukemia (CLL) has been thought to be the only leukemia subtype that is not related to radiation, risk for CLL was significantly increased at exposures above 50 WLM for radon and 20 mSv for gamma radiation versus below and in a continuous analysis. We have recently extended our analysis using different analytic approaches and considering additional cancer and mortality outcomes. Our overall aims were to evaluate mortality risks in the cohort, focusing on cancer and non-cancer outcomes using different methodological approaches to compare mortality in this cohort with that of the larger Czech population; to explore dose-related associations between radon exposure and cancer mortality within the cohort, and to explore risk for incident lung cancer in greater detail than had previously been reported - addressing confounding of the radon-lung cancer association by cigarette smoking and other co-pollutants and exploring potential additive or synergistic effects of smoking and radon. We reported (OEM 2019) that underground workers in the Pribram mines had higher rates of death due to all causes, all cancers, lung cancer and extrathoracic cancers compared to the population at large. Cancer incidence was similarly elevated overall and for lung and extrathoracic cancers as well as other sites not previously reported consistently. Analyses were carried out using Standardized Mortality Ratios and Causal Mortality Ratios which allowed us to explore years of life lost due to radon exposure and account for differential mortality patterns among miners as compared with the general population when evaluating risks for deaths from a specific cause. We also confirmed established radon-lung cancer associations, finding mortality effects that are consistent with established dose-response relationships for lung cancer while adding evidence at the lower end of the dose-response curve, demonstrating dose-response relationships for other cancer sites, and adding to the limited information on cancer incidence in miners exposed to radon. Additional manuscripts have been drafted and submitted for publication.