History of allergic diseases and lung cancer risk.

BACKGROUND The exact nature and direction of the association between a history of allergic diseases and lung cancer risk remain controversial. OBJECTIVE To examine the association between self-reported history of allergic diseases and lung cancer using data from a population-based case-control study conducted in the Montreal metropolitan area (1996-2002). METHODS The study is based on interview data collected from 1,169 incident lung cancer cases and 1,486 controls. Separate logistic regression models were used to estimate the relative risk of lung cancer, using odds ratios (ORs) and 95% confidence intervals (CIs), in subjects with vs without asthma, eczema, or hay fever after adjustment for several sociodemographic and lifestyle factors, including smoking. RESULTS For asthma, the OR was 0.90 (95% CI 0.65-1.24), which decreased to 0.76 (95% CI 0.54-1.08) for subjects whose onset was more than 2 years before lung cancer diagnosis or interview and then to 0.64 (95% CI 0.44-0.93) when restricted to subjects who reported using medication for their asthma. For eczema, the point estimate was 0.73 (95% CI 0.48-1.12), which decreased to 0.63 (95% CI 0.38-1.07) when considering eczema only in those who reported medication use. Hay fever showed the strongest inverse association with lung cancer (OR 0.37, 95% CI 0.24-0.59). CONCLUSION All 3 allergic diseases examined were inversely associated with lung cancer, although the strength of the protective effect varied. History of allergic diseases seems to have a protective role in lung cancer incidence, after consideration of potential confounders, including lifetime smoking history.