Occupational exposure to wood dust and risk of lung cancer in two population-based case-control studies in Montreal, Canada

Background: Wood dust is one of the oldest and one of the most common occupational exposures in the world. The present analyses examine the effect of lifetime exposure to wood dust in diverse occupational settings on lung cancer risk. Methods: We conducted two population-based case-control studies in Montreal: Study I (1979-1986) included 857 cases and two sets of controls (533 population and 1349 cancer controls), and Study II (1996-2001) comprised 736 cases and 894 population controls. Detailed job histories were obtained by interview and each job was evaluated by expert chemist-hygienists to estimate the likelihood and level of exposure to many substances, one of which was wood dust. Odds ratios (ORs) were computed in relation to different indices of exposure to wood dust, adjusting for several covariates including smoking. Three datasets were analysed: Study I with population controls, Study I with cancer controls, and Study II. Results: The most frequently exposed occupations in our study population were in construction, timber and furniture making industries. We found increased risks of lung cancer for substantial cumulative exposure to wood dust in Study I with cancer controls, (OR = 1.4: 95% confidence interval 1.0;-2.0) and in Study II (OR = 1.7: 95% confidence interval 1.1-2.7). There were no excess risks of lung cancer in any of the three datasets among workers whose cumulative exposure was not substantial. These tendencies held equally within strata of low smokers and heavy smokers. Conclusion: There was evidence of increased risk of lung cancer among workers with substantial cumulative exposure to wood dust.