Smoking and Glioma Risk: Evidence From a Meta-Analysis of 25 Observational Studies.

To systematically assess the relationship between smoking and glioma risk. A dose–response meta-analysis of case–control and cohort studies was performed. Pertinent studies were identified by searching database and reference lists. Random-effects model was employed to pool the estimates of the relative risks (RRs) with corresponding 95% confidence intervals (CIs). A total of 19 case–control and 6 cohort studies were included. Overall, compared with those who never smoked, the pooled RR and 95% CI was 0.98 (0.92–1.05) for ever smoker. The subgroups were not significantly different regarding risk of glioma except the group of age at start smoking (RR = 1.17, 95% CI: 0.93–1.48 for age < 20; RR = 1.25, 95% CI: 1.02–1.52 for age ≥ 20). Dose–response analysis also suggested no significant association between smoking and the risk of glioma, although some evidence for a linear relationship between smoking and glioma risk was observed. In conclusion, this meta-analysis provides little support for a causal relationship between smoking and risk of glioma.