Exposure To Radon And The Risk Of Lung Cancer By Histologic Group Among Canadian Uranium Miners

Abstract

Background: Underground uranium mining and milling was conducted in Ontario from 1954 to 1996. This study is an updated analysis of cancer incidence among male members of the Ontario Uranium Miner's Cohort exposed to radon daughters. Methods: The cohort was created using radon exposure and work history data collected during a government mandated chest x-rays program and by Canada's National Dose Registry. It consists of mine and mill workers who worked at least one week, with national mortality (1954-2007) and tumor registry (1969-2005) follow-up. Histologic groups were based on ICD-O-3; squamous cell carcinoma (SqCC), adenocarcinomas (ADC), small cell carcinoma (SmCC), large cell carcinoma (LCC), and other. Poisson regression was used to estimate relative risks (RRs) and their 95% confidence intervals (CIs) with levels of cumulative radon exposure. Results: Overall, 1,291 lung cancers were observed among 28,546 male cohort members with a mean of 21 WLM (range 0-875) of cumulative exposure. For histology-specific analysis there were 391 SqCC, 249 ADC, 225 LCC, and 181 SmCC lung cancers. For all lung cancers combined, an increasing risk was observed with cumulative radon exposures measured in Working Levels Months (WLM). The strongest associations were observed for SqCC and SmCC. In the highest exposure category (>60 Working Level Months) much stronger excess risks were observed for SqCC (RR=2.0, 95% CI=1.4-2.9) and SmCC (RR=2.1, 95% CI=1.3-3.5) than for ADC (RR=1.2, 95% CI=0.8-1.9) and LCC (RR=1.6, 95% CI=1.0-2.4), allowing for a 5-year lag of exposures. Conclusions: This study found higher relative risks for squamous and small cell carcinomas than for other histologic types and supports the limited evidence from other studies for histology-specific effects in radon induced lung cancer. Although limited by a lack of smoking data, the study has significant strengths including its quantitative exposure assessment, access to national tumor registry data, and large size.