Background In 2004, Ireland became the first country to institute a comprehensive workplace smoking ban. Previous research has found that comprehensive smoking bans are associated with public health benefits. However, given the relative recency of smoking bans and the long latency of the effect of cigarette smoke on lung cancer, the effect of smoking bans on lung cancer has not been well explored.

Methods An appropriate lag time for the smoking ban was calculated (2010 for lung cancer incidence, 2006 for lung cancer mortality). Using these breakpoints, a one-sample, Poisson-based, interrupted time series analysis was used to compare lung cancer incidence and mortality before and after the modelled interruptions. An identical analysis was applied to brain cancer, a cancer with no known link to smoking or second-hand smoke exposure, as a validity check.

Results Each year following the modelled interruptions, lung cancer incidence and mortality in Ireland decreased 2% (95%CI 1–3, p<0.01) and 1% (95%CI 0–2, p=0.02) relative to the modelled counterfactual. In absolute terms, the smoking ban was associated with 32 (95%CI 14–52) fewer lung cancer incident cases per year and 113 (95%CI 96–131) fewer lung cancer deaths per year, equivalent to 1.36% of the post-interruption lung cancer incident cases and 6.03% of the post-interruption lung cancer deaths.

Discussion The 2004 Irish Workplace Smoking Ban avoided approximately 195 incident lung cancer cases and 1,125 lung cancer deaths to by 2015. This is among the first quasi-experimental studies to examine the effect of a comprehensive smoke-free policy on lung cancer.