Multiplicity of abnormal promoter methylation in lung adenocarcinomas from smokers and never smokers

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Abstract
The prevalence of methylation of the p16, DAPK and RASSF1A genes was investigated in lung adenocarcinoma from smokers, former uranium miners and never smokers. The association between a common genetic alteration in adenocarcinoma, mutation of the K‐ras gene and methylation of these genes, as well as survival was examined. Adenocarcinomas from 157 smokers, 46 never smokers and 34 former uranium miners were evaluated for methylation of the p16, DAPK and RASSF1A genes using the methylation‐specific PCR assay. Comparisons were also made to prevalences of methylation of the MGMT gene and mutation of the K‐ras gene previously examined in these tumors. The prevalence of methylation for all genes was similar between adenocarcinomas from smokers and never smokers, although the prevalence for methylation of the p16 gene tended to be higher in smokers compared to never smokers. A significantly higher prevalence for p16 methylation was seen in central vs. peripheral lung tumors. At least 1 gene was methylated in 35% of stage I tumors, whereas 2 and ≥3 genes were methylated in 40% and 16% of tumors, respectively. Methylation of all genes was independent of K‐ras mutation, whereas methylation of the DAPK and RASSF1A genes was positively associated. Environmental tobacco smoke, the strongest lung cancer risk factor among never smokers, induces adenocarcinoma in part through inactivation of the p16, DAPK and RASSF1A genes. Adenocarcinomas may develop through 2 distinct processes: multiple gene inactivations through promoter hypermethylation and activation of the K‐ras gene.