Gastroenterology

Gastroenterology

Volume 122, Issue 5, May 2002, Pages 1376-1387
Gastroenterology

Basic Research
CpG island methylation in sporadic colorectal cancers and its relationship to microsatellite instability

https://doi.org/10.1053/gast.2002.32997Get rights and content

Abstract

Background & Aims: Methylation of CpG islands is increasingly recognized as an important event in colorectal carcinogenesis. We evaluated the extent of CpG island methylation in 426 sporadic colorectal cancers to define its relationship to microsatellite instability and to describe its clinicopathologic and genetic features. Methods: Fresh cancer tissue was obtained from 417 consecutive individuals undergoing curative surgery for sporadic colorectal cancer. Methylation of p16 and hMLH1 promoters was determined by methylation-specific polymerase chain reaction (PCR), whereas methylation at MINT 1, 2, 12, and 31 loci was assessed by bisulfite PCR. Microsatellite instability and K-ras and p53 status were determined using microsatellite PCR, restriction enzyme–mediated PCR, and immunohistochemistry, respectively. Results: Individual loci were commonly methylated, but locus-specific phenotypic changes were not seen. CpG island methylation was associated with right-sided location, female sex, and older age, as well as high tumor grade, mucinous type, wild-type P53, microsatellite instability, and K-ras mutations. More than half of tumors showing CpG island methylation were microsatellite stable. Compared with microsatellite unstable cancers, they were more commonly left-sided, had fewer intraepithelial lymphocytes, presented later, and had a worse outcome. Conclusions: Colorectal cancers with CpG island methylation have distinct clinicopathologic features and in some cases lead to sporadic microsatellite unstable cancers.

GASTROENTEROLOGY 2002;122:1376-1387

Section snippets

Patients and specimens

After obtaining informed consent, 417 consecutive individuals (with 426 colorectal tumors) undergoing surgical resection of adenocarcinoma of the colon or rectum at St. Vincent's Hospital, Sydney, were enrolled in this prospective study from 1993 to January 2001. Patients with inflammatory bowel disease or a known history of familial adenomatous polyposis or hereditary nonpolyposis coli were excluded from the study.19 Fresh representative tissue samples (500 μg) from all tumors and paired

Assessment of CpG island methylation

The typical results of PCR analysis of bisulfite-treated DNA for methylation of MINT loci as well as p16 are shown in Figure 1.

. Analysis of methylation of hMLH1, p16, and the MINT loci in colorectal tumors. For p16 and hMLH1 promoter analysis, bisulfite-modified tumor DNA was amplified in separate reactions using primers specific for unmethylated or methylated template (methylation-specific PCR). Reactions using methylation-specific primers are designated with ~ for p16 and * for hMLH1. Tumor

Discussion

This study considers the frequency and extent of CpG island methylation in a large consecutive group of sporadic colorectal cancers and provides information on the features of tumors showing this phenomenon as well as the interaction between this event and the development of MSI.

Acknowledgements

The authors thank Rachael Williams for her assistance in the collection and verification of family history and survival data, Dr. Matthew Law for advice on statistics, Dr. Jenny Turner for review of histopathologic specimens, and Dr. Alison Todd for technical advice related to the optimization of the p16 MSP assay.

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    Address requests for reprints to: Robyn Ward, M.D., Department of Medical Oncology, St. Vincent's Hospital, Victoria Street, Darlinghurst 2010, Australia. e-mail: [email protected]; fax: (612) 83823386.

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