However, only four of the previously reported associations with polymorphisms in the GSTP1 (Ala14Val), SOD2 (Val16Ala), EPHX1 (His139Arg) genes and the NAT1 fast acetylator phenotype remained significantly associated with lung cancer.
A genetic component of early-onset lung cancer has been suggested but variations in enzyme activity and polymorphisms in EPHX1 have seldom been studied in young patients with lung cancer.
ETS-exposed individuals (both active and passive smokers) who carried the His allele of mEH exon3 have a 2.9-fold increased risk of lung cancer (odds ratio [OR] 2.9, P < 0.001).
In conclusion, the CA data provides evidence to support that susceptibility mEH alleles are significantly involved with the development of lung cancer from cigarette smoking.
A combination of susceptible CYP1A1 and HYL1 genotypes was found to be highly associated with lung cancer, especially with SCC (OR 6.76; 95% CI 2.29-19.10).
To determine whether there is gene-environment interaction between NAT2 polymorphisms, alone or in combination with mEH polymorphisms, and cumulative smoking exposure in the development of lung cancer, we conducted a case control study of 1115 Caucasian lung cancer patients and 1250 spouse and friend controls.
Our results showed that the variant allele of mEPHX exon 4 increased the overall lung cancer risk by 56% (odds ratio [OR]=1.56, 95% confidence interval [CI]=0.99-2.46).
Among genetic polymorphisms reviewed here, myeloperoxidase gene (a G to A mutation) and microsomal epoxide hydrolase exon 4 polymorphism (substitution of Arg for His) were significantly associated with lung cancer risk.
Together with data from the present study on DNA repair genes, we did not observe significant associations between any single variant genotype for several DNA-repair and chemical-metabolizing genes (XPD [or ERCC2], XRCC1, XRCC3, GSTM1, GSTT1, MPO, and mEH [or EPHX1]) and lung cancer.
When the exon 3 and 4 polymorphisms were considered together, the combined EPHX1 His113His113/His139His139 genotype (very low predicted enzyme activity) was found to be associated with an increased risk of lung cancer (P = 0.044, OR = 3.063, CI = 0.932-10.069).
Our results agree with these observations in vitro and suggest that a genetically determined combination of a high-activity mEH and a low-activity GSTpi may increase lung cancer risk among smokers.
This current meta-analysis suggests that EPHX1T113C polymorphism is associated with lung cancer risk, and there is an obvious race-specific effect in the association.
MDR analysis identified two distinct predictor models for the risk of lung cancer in smokers (tobacco chewing, EPHX1Tyr113His, and SULT1A1 Arg213His) and non-smokers (CYP1A1*2A, GSTP1 Ile105Val and SULT1A1 Arg213His) with testing balance accuracy (TBA) of 0.6436 and 0.6677 respectively.
We searched for associations with the 'sum of at-risk alleles' by combining the variant alleles of EPHX1, NQO1 and MnSOD(2) together with the wild-type allele of APE1, since they appeared to influence lung cancer risk.