Risk of lung cancer following nonmalignant respiratory conditions: evidence from two case-control studies in Montreal, Canada.

There has been conflicting evidence concerning possible associations between several nonmalignant respiratory diseases and subsequent risk of lung cancer. In the context of two large population based case-control studies of lung cancer carried out in Montreal, we were able to study the possible relationships between a previous history of lung disease and subsequent risk of lung cancer. Interviews for Study I were conducted in 1979-1986 (755 cases and 512 controls) and included questions on asthma and tuberculosis. Interviews for Study II were conducted in 1996-2001 (1205 cases and 1541 controls) and included questions on asthma, tuberculosis, emphysema, and pneumonia. Lung cancer risk was analysed in relation to each condition, adjusting for several potential confounders, including smoking in a three-variable parametrization. To avoid any possible confusion between the respiratory conditions and early symptoms of lung cancer, conditions occurring in the 3 years before diagnosis of cancer were discounted. For asthma there was no evidence of an association. For TB the evidence was inconsistent between Study I and Study II. For both pneumonia and emphysema, there were significantly elevated odds ratios, with point estimates in the range of 1.6-2.4. Our results support the hypothesis that some nonmalignant respiratory diseases may be independent risk factors for lung cancer.