Objectives Workplace environmental tobacco smoke (ETS) was historically a prevalent lung carcinogen in Canada, and remains a hazard in certain occupations. This study estimates the attributable fraction (AF) of lung cancers due to workplace ETS, and is part of a larger effort to estimate the current burden of occupational cancers in Canada.

Methods The AF calculation requires estimates of the proportion of workers ever exposed (PrE) during the risk exposure period (REP, 1961 – 2000) and the relative risk (RR). To estimate the PrE, the proportion of never-smokers who were exposed to workplace ETS was calculated from Canadian data sources, then combined with historical Canadian employment statistics, labour force data and survival probabilities. Exposure duration was estimated using data from a national case-control study, and used to assign RRs based upon a dose-response relationship reported in the literature. We accounted for never-smoking lung cancer cases, using rates observed among never-smokers in a large US study (CPS-II).

Results The proportion of never-smokers in men showed an increasing trend during the REP while in women the proportion decreased slightly. A drop in the proportion of workers exposed to workplace ETS was found in the 80’s and 90’s. Approximately 7.2 million workers were ever exposed to workplace ETS during the REP, of which half were female. Estimated AFs for ETS-related lung cancers were: 0.6% for males, and 0.5% for females, which equates to 74 lung cancer cases in men and 57 in women. This translates to AFs of 11.8% and 5.8% among never-smoking men and women, respectively.

Conclusions Lung cancer attributable to workplace ETS was low in the Canadian population because a large proportion of lung cancer cases occurred among current or former smokers. When only considering the burden among never-smokers, we found a relatively large proportion of cases attributable to workplace ETS.