title: Mutational and epigenetic evidence for independent pathways for lung adenocarcinomas arising in smokers and never smokers.
abstract: Genetic and epigenetic alterations are considered to play important roles in lung cancer. Recent studies showed that EGFR and K-RAS mutations exhibited a mutually exclusive pattern in adenocarcinoma of the lung, suggesting the presence of two independent oncogenic pathways. However, it is unknown how epigenetic alterations were involved in lung carcinogenesis mediated by EGFR or K-RAS mutation. In this study, we examined the relationship between genetic and epigenetic alterations in 164 cases of lung adenocarcinoma. Somatic mutations were determined by direct sequence of EGFR exons 18 to 21 and K-RAS codons 12 and 13. Methylation status of p16(INK4a), RASSF1A, APC, RARbeta, and CDH13, frequently methylated in lung cancer, was determined by methylation-specific PCR and the degree of methylation was defined as the methylation index. Multivariate analysis adjusted for age, sex, and smoking dose showed that the probability of having EGFR mutation was significantly lower among those with p16(INK4a) and CDH13 methylation than in those without [p16(INK4a): odds ratio (OR), 0.07; 95% confidence interval (95% CI), 0.02-0.33; CDH13: OR, 0.34; 95% CI, 0.15-0.77] and the methylation index was significantly lower in EGFR mutant cases than in wild type (OR, 0.70; 95% CI, 0.52-0.95). By contrast, K-RAS mutation was significantly higher in p16(INK4a) methylated cases than in unmethylated cases (OR, 4.93; 95% CI, 1.54-15.7) and the methylation index was higher in K-RAS mutant cases than in wild type with marginal significance (OR, 1.46; 95% CI, 0.95-2.25). Our results indicate the differences in the evolvement of epigenetic alterations between the EGFR- and K-RAS-mediated tumorigenesis and suggest the specific interaction of genetic and epigenetic changes in tumorigenesis of lung cancer.
authors.affiliation: Department of Cancer and Thoracic Surgery, Graduate School of Medicine and Dentistry, Okayama University, 2-5-1 Shikata-cho, Okayama 700-8558, Japan. s_toyooka@nigeka2.hospital.okayama-u.ac.jp
authors.forename: Shinichi
authors.initials: S
authors.lastname: Toyooka
authors.forename: Masaki
authors.initials: M
authors.lastname: Tokumo
authors.forename: Hisayuki
authors.initials: H
authors.lastname: Shigematsu
authors.forename: Keitaro
authors.initials: K
authors.lastname: Matsuo
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Asano
authors.forename: Kunitoshi
authors.initials: K
authors.lastname: Tomii
authors.forename: Shuji
authors.initials: S
authors.lastname: Ichihara
authors.forename: Makoto
authors.initials: M
authors.lastname: Suzuki
authors.forename: Motoi
authors.initials: M
authors.lastname: Aoe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Date
authors.forename: Adi F
authors.initials: AF
authors.lastname: Gazdar
authors.forename: Nobuyoshi
authors.initials: N
authors.lastname: Shimizu
mesh_terms: D000230:Adenocarcinoma / Q000209:etiology* / Q000235:genetics*; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D016147:Genes, Tumor Suppressor; D018773:Genes, erbB-1 / Q000235:genetics; D011905:Genes, ras / Q000235:genetics; D006801:Humans; D008175:Lung Neoplasms / Q000209:etiology* / Q000235:genetics*; D008297:Male; D009154:Mutation; D012907:Smoking / Q000009:adverse effects* / Q000235:genetics*