To investigate the role of
microsomal epoxide hydrolase (mEH) polymorphisms in the aetiology of
lung cancer and to assess the interaction between mEH polymorphisms and smoking, we performed a meta-analysis of seven published studies, which included 2078 cases and 3081 controls, and a pooled analysis of eight studies (four published and four unpublished at that time) with a total of 986 cases and 1633 controls. The combined meta-analysis odds ratios (
ORs) were 0.98 (95% confidence interval [CI] = 0.72-1.35) for polymorphism at
amino acid 113 in exon 3 (
His/His versus
Tyr/Tyr genotype) and 1.00 (95% CI = 0.71-1.41) for polymorphism at
amino acid 139 in exon 4 (
Arg/Arg versus
His/His genotype). In the pooled analysis, we observed a significant decrease in
lung cancer risk (OR = 0.70, 95% CI = 0.51-0.96) for exon 3
His/His genotype after adjustment for age, sex, smoking and centre. The protective effect of exon 3 polymorphism seems stronger for
adenocarcinoma of the lung than for other histological types. The OR for high predicted mEH activity, compared with low activity, was 1.54 (95% CI = 0.77-3.07) in the meta analysis and 1.18 (95% CI = 0.92-1.52) in the pooled analysis. We did not find a consistent modification of the carcinogenic effect of smoking according to mEH polymorphism, although the risk of
lung cancer decreased among never smokers with high mEH activity and among heavy smokers with the exon 3
His/His genotype. In conclusion, this study suggests a possible effect of mEH polymorphisms at exon 3 in modulating
lung cancer. If present, this effect may vary among different populations, possibly because of interaction with genetic or environmental factors.