Background: Radon at sufficiently high concentrations is known to cause lung cancer among underground miners and in experimental laboratory animals.
Purpose: Our aim was to determine whether indoor levels of radon are associated with a detectable increase in lung cancer. Nonsmoking women were selected because they offer the best opportunity to detect radon-related risk while minimizing the potentially confounding influences of cigarette smoking and occupation.
Methods: A population-based, case-control study of incident lung cancer was conducted in Missouri. A total of 538 non-smoking white women diagnosed with lung cancer between 1986 and 1992 and 1183 age-matched control subjects were identified from the Missouri Cancer Registry and from driver's license and Medicare listings, respectively. Information on lung cancer risk factors was obtained by telephone interview. Year-long radon measurements were sought in every dwelling occupied for the previous 5-30 years.
Results: Radon measurements covered 78% of the relevant residential period, and women reported being indoors for 84% of this time. The time-weighted average radon concentrations were exactly the same for case subjects and control subjects (1.82 pCi/L of air [pCi L-1]). Radon levels greater than 4 pCi L-1 were experienced by 6.5% of the case subjects and 6.8% of the control subjects. For all data combined, there was little evidence for a trend of lung cancer with increasing radon concentrations (two-tailed trend test, P = .99 continuous data analysis; P = .19 categorical data analysis). A positive dose-response trend was suggested for the adenocarcinoma cell type and among directly interviewed women (two-tailed trend test; P = .31 continuous data analysis; P = .04 categorical data analysis), but not for other histologies or among those who had surrogate interviews.
Conclusions: The possibility of detecting a risk from indoor radon in this study was maximized by (a) including a large number of nonsmoking women with high indoor occupancy, (b) conducting a large number of radon measurements near the time of the diagnosis of cancer, and (c) controlling for known causes of lung cancer. However, an association between lung cancer and the exposure to domestic levels of radon was not convincingly demonstrated.
Implications: The magnitude of the lung cancer risk from radon levels commonly found in U.S. dwellings appears low.