A meta-analysis of asthma and risk of lung cancer (United States)

Objective: To review epidemiologic evidence that asthma is a risk factor for lung cancer, with particular attention to the role of smoking on this association. Methods: Through MEDLINE computer searches (January 1966 to April 2002) and a review of references, we identified studies with quantitative data on the relation of asthma to lung cancer. Summary estimates of relative risks (RR) were calculated using the fixed-effects model or the random-effects model as appropriate. Results: The combined results from five case–control studies – that presented data limited to individuals who had never smoked – showed a 1.8-fold increase in lung cancer risk among asthmatics (95% confidence interval (CI) = 1.3–2.3). The results from six case–control and four cohort studies, which controlled for smoking history also were significant (RR = 1.7; 95% CI = 1.3–2.2). Finally, to illustrate the potential confounding by tobacco, we combined data from seven cohort studies that did not control for smoking history and found an overall RR of 1.4 (95% CI = 1.2–1.6). Conclusions: The increased risk of lung cancer among never smoking individuals with asthma supports a direct relation between asthma and lung cancer. There is biological evidence to support this association.