Residential radon exposure and lung cancer: an overview of published studies

A possible link between presumed or measured household radon exposure and lung cancer is reviewed on the basis of published epidemiologic studies. Evidence of a link is reported as a result of studies in Sweden; findings are inconsistent elsewhere. A number of methodological problems were found. Many of the studies are ecological in design and are, therefore, primarily hypothesis generating. A number of studies lack any data on the number of lung cancers and are, therefore, difficult to evaluate. Some other studies provide results that are internally inconsistent. Of the case/control studies, there are many with minimal or no information on active and passive smoking, occupation, family history of cancer, and diet. The case/control studies are generally small in size and of low statistical power. Exposure classifications are nonstandardized, inconsistent in their findings, and often gross in their characterization of radon concentrations. Relatively few of the studies actually measured radon exposure. Some of the studies showed significant positive associations either with geological characteristics, water supply contamination, or house type. No significant associations were found with residence near uranium or radium processing waste. Where radon levels were measured, a relatively small percentage of studies found a statistically significant positive association with lung cancer. Overall, the evidence for an association between residential radon exposure and lung cancer is weak. There is a need for a more decisive case/control epidemiologic study of this problem.