Objectives To determine whether exposure to various chlorinated solvents is associated with lung cancer.

Methods Two case–control studies of occupation and lung cancer were conducted in Montreal, and included 2016 cases and 2001 population controls. Occupational exposure to a large number of agents was evaluated using a combination of subject-reported job history and expert assessment. We examined associations between lung cancer among men and six specific chlorinated solvents and two chemical families (chlorinated alkanes and alkenes). ORs were calculated using unconditional multivariate logistic regression.

Results When the two studies were pooled, there were indications of an increased risk of lung cancer associated with occupational exposure to perchloroethylene (OR_{any exposure} 2.5, 95% CI 1.2 to 5.6; OR_{substantial exposure} 2.4, 95% CI 0.8 to 7.7) and to carbon tetrachloride (OR_{any exposure} 1.2, 95% CI 0.8 to 2.1; OR_{substantial exposure} 2.5, 95% CI 1.1 to 5.7). No other chlorinated solvents showed both statistically significant associations and dose–response relationships. ORs appeared to be higher among non-smokers. When the lung cancer cases were separated by histological type, there was a suggestion of differential effects by tumour type, but statistical imprecision and multiple testing preclude strong inferences in this regard.

Conclusions There were suggestive, albeit inconsistent, indications that exposure to perchloroethylene and carbon tetrachloride may increase the risk of lung cancer. Results for other solvents were compatible with absence of risk.