MGMT promoter methylation and field defect in sporadic colorectal cancer

J Natl Cancer Inst. 2005 Sep 21;97(18):1330-8. doi: 10.1093/jnci/dji275.

Abstract

Background: Sporadic colorectal cancers often arise from a region of cells characterized by a "field defect" that has not been well defined molecularly. DNA methylation has been proposed as a candidate mediator of this field defect. The DNA repair gene O6-methylguanine-DNA methyltransferase (MGMT) is frequently methylated in colorectal cancer. We hypothesized that MGMT methylation could be one of the mediators of field cancerization in the colon mucosa.

Methods: We studied MGMT promoter methylation by three different bisulfite-based techniques in tumor, adjacent mucosa, and non-adjacent mucosa from 95 colorectal cancer patients and in colon mucosa from 33 subjects with no evidence of cancer. Statistical tests were two-sided.

Results: MGMT promoter methylation was present in 46% of the tumors. Patients whose cancer had MGMT promoter methylation also had substantial MGMT promoter methylation in apparently normal adjacent mucosa. This methylation was seen with a quantitative assay in 50% (22/44; 95% confidence interval [CI] = 34% to 65%) of normal samples with MGMT promoter methylation in the adjacent tumors, 6% (3/51; 95% CI = 1% to 16%) of samples without MGMT methylation in adjacent tumors, and 12% (4/33; 95% CI = 3% to 28%) of control samples (P < .001 for comparison between each of the latter two groups and the first group). MGMT methylation was detected with a more sensitive assay in 94%, 34%, and 27% of these samples, respectively (P < .001). In grossly normal colonic mucosa of colon cancer patients, methylation was detected 10 cm away from the tumor in 10 of 13 cases. Tumors with MGMT promoter methylation had a higher rate of G-to-A mutation in the KRAS oncogene than tumors without MGMT promoter methylation (10/42 versus 3/46, P = .03). Using a sensitive mutant allele-specific amplification assay for KRAS mutations, we also found KRAS mutations in 12% (3/25; 95% CI = 2.5% to 31%) of colorectal mucosas with detectable MGMT methylation and 3% (2/64; 95% CI = 0.4% to 11%) of colorectal mucosas without MGMT methylation (P = .13).

Conclusion: Some colorectal cancers arise from a field defect defined by epigenetic inactivation of MGMT. Detection of this abnormality may ultimately be useful in risk assessment for colorectal cancer.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Biomarkers, Tumor / genetics*
  • Cell Line, Tumor
  • Colorectal Neoplasms / enzymology
  • Colorectal Neoplasms / genetics*
  • Colorectal Neoplasms / pathology
  • DNA Methylation*
  • Epigenesis, Genetic
  • Gene Silencing*
  • Humans
  • Intestinal Mucosa / enzymology*
  • Intestinal Mucosa / pathology
  • Mutation
  • O(6)-Methylguanine-DNA Methyltransferase / genetics*
  • Polymerase Chain Reaction / methods
  • Promoter Regions, Genetic*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins p21(ras)
  • Risk Factors
  • Sensitivity and Specificity
  • Sequence Analysis, DNA
  • Sulfites
  • Tumor Suppressor Protein p53 / genetics
  • ras Proteins

Substances

  • Biomarkers, Tumor
  • KRAS protein, human
  • Proto-Oncogene Proteins
  • Sulfites
  • Tumor Suppressor Protein p53
  • O(6)-Methylguanine-DNA Methyltransferase
  • Proto-Oncogene Proteins p21(ras)
  • ras Proteins
  • hydrogen sulfite