Journal of Experimental & Clinical Cancer Research 2009, 28:153 http://www.jeccr.com/content/28/1/153 the ERCC2 751Lys/Gln, 312Asp/Asn, and ERCC1 118Asn/Asn were 751 F5'-GCC CGC TCT GGA TTA TAC G-3' and R5'-CTA TCA TCT CCT GGC CCC C-3', 312 F5'- CTG TTG GTG GGT GCC CGT ATC TGT TGG TCT-3' and R5'-TAA TAT CGG GGC TCA CCC TGC AGC ACT TCC T- 3', 118 F5'-AGG ACC ACA GGA CAC GCA GA-3' and R5'- CAT AGA ACA GTC CAG AAC AC-3', respectively. The PCR products were digested with restriction enzyme (New England Biolabs, Beverly, MA) PstI (for Lys751Gln), StyI (for Asp312Asn), and BsrdI (for Asn118Asn) to determine the genotypes. A 10% masked, random sample of patients was tested twice by different persons, and the results were found to be concordant for all of the masked duplicate sets. Statistical analysis All statistical analyses were performed with Statistical Product and Service Solutions (SPSS) v13.0, if not other- wise specified. All of the tests were two-sided, and statisti- cal significance was defined as P < 0.05. Pearson's chi- square test was used to compare the distribution of the demographic variables and examine differences in risk factors and genotypes, alleles and haplotypes between cases and controls. Hardy-Weinberg equilibrium (HWE) of the genotypes was tested by performing a goodness-of- fit χ2 test. Unconditional logistic regression analysis was performed to calculate the odds ratios (ORs) with 95% confidence intervals (CIs) for estimating the association between certain genotypes and lung cancer. The stratified analyses and gene-environment interaction were evalu- ated by logistic regression models. On the basis of the observed frequencies of three SNPs, we used the SHEsis analysis platform to calculate linkage disequilibrium index (D' and r2) and infer haplotype frequencies [6,7]. Results Selected demographic variables and environmental risk factors for the 285 patients and 285 controls were listed in Table 1. All subjects were females and all cases were lung adenocarcinoma patients. Mean ages of cases and controls Table 1: Selected variable in cases and controls (mean ± S.D.) were almost identical (53.9 ± 12.0 and 54.1 ± 9.1 years, respectively). There were no significant differ- ences in the distribution of family history of cancer, pas- sive smoking, fuel smoke exposure, occupational exposures, and dietary habits between cases and controls. However the cases were more likely than the controls to report cooking oil fume exposure (OR 1.61, 95%CI 1.13- 2.30, P = 0.009). Table 2 presents the distribution of ERCC2 751, 312 and ERCC1 118 polymorphisms in cases and controls. The fre- quencies of the 751C, 312A and 118T allele in the con- trols were 0.08, 0.05 and 0.21, respectively. All allele distributions were consistent with Hardy-Weinberg equi- librium. Among these SNPs, heterozygous carriers of the ERCC2 751AC genotype had a 1.66-fold risk of lung ade- nocarcinoma compared with those carrying the homozygous wild genotype (95%CI 1.07-2.59, P = 0.024). Individuals carrying ERCC1 118TT homozygote genotype had a 2.01-fold (marginally significant) increased risk of cancer compared with the wild genotype (95%CI 0.99-4.10, P = 0.054). ERCC2 312 polymorphism was not associated with risk of lung adenocarcinoma in this study. Considering the problem of sample size, fur- ther analyses were carried on by combining the hetero- zygous variant genotype with the homozygous variant genotype in three polymorphisms. As a result, the com- bined ERCC2 751AC/CC was associated with an increased risk of lung adenocarcinoma with an adjusted OR of 1.64 (95%CI 1.06-2.52, P = 0.025). In the stratified analyses, we found that the increased risk associated with ERCC2 751 variant genotypes (AC/CC) was more pronounced in individuals without exposure to cooking oil fume (OR 1.98, 95%CI 1.18-3.32, P = 0.010) and those without exposure to fuel smoke (OR 2.47, 95%CI 1.46-4.18, P = 0.001) (Table 3). Stratified by other environmental exposures, no statistically significant rela- tionships were suggested (data not shown). We evaluated the interaction of genetic polymorphism with cooking oil Variable Female Age (years) Income(yuan/month) Education Never Elementary school Junior school Senior school and upwards Family history of cancer Passive smoking Fuel smoke exposure Cooking oil fume exposure Cases n (%) 285 53.9 ± 12.0 619.34 ± 374.59 27 (9.5) 133 (46.7) 85 (29.8) 40 (14.0) 39 (13.7) 174 (61.1) 84 (29.5) 104 (36.5) Controls n (%) 285 54.1 ± 9.1 557.11 ± 390.61 26 (9.1) 145 (50.9) 76 (26.7) 38 (13.3) 27 (9.5) 162 (56.8) 78 (27.4) 75 (26.3) P value 0.750 0.071 0.779 0.116 0.307 0.577 0.009 Page 3 of 7 (page number not for citation purposes)