title: CpG island methylation of genes accumulates during the adenoma progression step of the multistep pathogenesis of colorectal cancer.
abstract: Genetic alterations occur during the adenoma-carcinoma sequence of colon cancer formation and drive the initiation and progression of colon cancer formation. The aberrant methylation of genes is an alternate, epigenetic mechanism for silencing tumor suppressor genes in colon cancer. The aim of this study was to determine on a global and gene-specific level the role of CpG island methylation in the initiation and progression of colon cancer. Consequently, we assessed the frequency of gene methylation in tumors representative of the commonly recognized histological steps of the adenoma-carcinoma progression sequence through the analysis of eight genes previously identified to be methylated in colon cancer, MGMT, HLTF, MLH1, p14(ARF), CDKN2A, TIMP3, THBS1, and CDH1. We observed that the proportion of tumors carrying methylated alleles increased from adenomas to adenocarcinomas but that the proportion of tumors with methylated alleles was not different between adenocarcinomas and metastases (69% versus 90%, P = 0.01 and 90% versus 81%, P > 0.05). The most substantial difference occurred between early and advanced adenomas (47% versus 84%, P = 0.018). Furthermore, we observed that the frequency of gene methylation at the different steps of the progression sequence varied between genes. Thus, the aberrant methylation of genes appears to increase most significantly during the progression of early adenomas to advanced adenomas, and the frequency of specific gene methylation at the different steps of the adenoma-carcinoma progression sequence varies in a gene-specific fashion.
authors.affiliation: Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
authors.forename: Young-Ho
authors.initials: YH
authors.lastname: Kim
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Petko
authors.forename: Slavomir
authors.initials: S
authors.lastname: Dzieciatkowski
authors.forename: Li
authors.initials: L
authors.lastname: Lin
authors.forename: Mahan
authors.initials: M
authors.lastname: Ghiassi
authors.forename: Steve
authors.initials: S
authors.lastname: Stain
authors.forename: William C
authors.initials: WC
authors.lastname: Chapman
authors.forename: Mary Kay
authors.initials: MK
authors.lastname: Washington
authors.forename: Joseph
authors.initials: J
authors.lastname: Willis
authors.forename: Sanford D
authors.initials: SD
authors.lastname: Markowitz
authors.forename: William M
authors.initials: WM
authors.lastname: Grady
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism; D000236:Adenoma / Q000235:genetics* / Q000473:pathology; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology / Q000556:secondary; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation; D018450:Disease Progression; D005260:Female; D005787:Gene Frequency; D052138:Genes, Neoplasm; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000556:secondary; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis