Relationship between cigarette smoking and risk of chronic myeloid leukaemia: a meta-analysis of epidemiological studies

Objective: Previous epidemiologic studies that have been reported on the association between cigarette smoking and risk of chronic myeloid leukaemia (CML) have remained controversial. A comprehensive meta-analysis was performed to evaluate smoking as a potential relationship factor and incidence of CML. Methods: Systematic literatures collected from articles published before August 2015 were searched from PubMed, EMBASE and the Cochrane Library. A total of 10 studies (nine case-controls and one cohort) met inclusion criteria of this meta-analysis. Odds ratios (ORs) with 95% confidence interval (CI) were calculated to assess the strength of the association between cigarette smoking and risk of CML in this study. Quality assessments were performed on the studies with the Newcastle-Ottawa Scale. I2 index was used to evaluate heterogeneity. Finally, publication bias was assessed through funnel plots and Begger's test. Results: No significant association was observed between ever-smokers and CML when compared among non-smokers (OR=1.13, 95% CI: 0.99-1.29) or between subgroups stratified by smoking history, gender, geographical region, study design and source of patients. Our results demonstrate that this association was stronger in individuals who smoked <20 cigarettes/day (OR=1.72, 95% CI: 1.06-2.79) vs. individuals who smoked >20 cigarettes/day (OR=1.24, 95% CI: 0.55-2.81). Moreover, cumulative smoking of <15, 15-30 and >30 pack-years was associated with ORs of 1.22, 1.32 and 1.39, respectively (P<0.001, for trend). Conclusion: This meta-analysis suggests that smoking may significantly increase the risk of CML in a dose-dependent manner. However, additional well-designed, prospective cohort studies are required to verify these findings and identify other risk factors associated with CML.