Objective The long-term risks of lung cancer from radon progeny exposure are known largely from studies of uranium miners, including a cohort of 4137 male miners from the Colorado Plateau (CP) in the southwestern US. Our objective was to estimate the excess absolute risk (EAR) and excess relative risk (ERR) of lung and other cancer from radon exposure among CP uranium miners, evaluating the persistence of risk with 26 years of extended follow-up, and the form of interaction between radon and cigarette pack-years (PY).

Methods We followed the CP cohort for mortality through 2016, re-evaluated its radon exposure against original records, and imputed a smoking end date for cohort members. We evaluated EAR based on standardized rate ratios of lung cancer, adjusted for age, calendar year, and race. We modeled ERR using Cox proportional hazards regression of full risk sets (adjusted for age, race, birth year, exposure rate and time since last exposure). We also modeled variation in risk per unit exposure by attained age (AA) and time-since-exposure (TSE) and evaluated joint effects of radon and PY.

Results We identified 695 cases of lung cancer, including 146 among never- and light smokers. Lung cancer EAR per unit radon exposure increased substantially with smoking PY and throughout decades of follow-up. Lung cancer ERR decreased with AA and TSE, although to a lesser extent than observed elsewhere. The form of interaction between radon and PY was sub-multiplicative but greater-than-additive, appearing closer to multiplicative at lower radon exposures. Pancreas was the only other site showing a significantly positive ERR per unit exposure, although much lower than for lung cancer.

Conclusion Excess risk of lung cancer persists throughout the lifespan among this cohort of uranium miners. Information about radon-smoking interactions, particularly at low exposure levels, is of interest for extrapolations to the general population.