Smoking as a risk factor for lung cancer in women and men: a systematic review and meta-analysis

ObjectivesTo investigate the sex-specific association between smoking and lung cancer.DesignSystematic review and meta-analysis.Data sourcesWe searched PubMed and EMBASE from 1 January 1999 to 15 April 2016 for cohort studies. Cohort studies before 1 January 1999 were retrieved from a previous meta-analysis. Individual participant data from three sources were also available to supplement analyses of published literature.Eligibility criteria for selecting studiesCohort studies reporting the sex-specific relative risk (RR) of lung cancer associated with smoking.ResultsData from 29 studies representing 99 cohort studies, 7 million individuals and >50 000 incident lung cancer cases were included. The sex-specific RRs and their ratio comparing women with men were pooled using random-effects meta-analysis with inverse-variance weighting. The pooled multiple-adjusted lung cancer RR was 6.99 (95% Confidence Interval (CI) 5.09 to 9.59) in women and 7.33 (95% CI 4.90 to 10.96) in men. The pooled ratio of the RRs was 0.92 (95% CI 0.72 to 1.16; I2=89%; p