MGMT promoter methylation and field defect in sporadic colorectal cancer.
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).


CONCLUSIONS
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.
Shen
Lanlan
L
Department of Leukemia, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Kondo
Yutaka
Y
Rosner
Gary L
GL
Xiao
Lianchun
L
Hernandez
Natalie Supunpong
NS
Vilaythong
Jill
J
Houlihan
P Scott
PS
Krouse
Robert S
RS
Prasad
Anil R
AR
Einspahr
Janine G
JG
Buckmeier
Julie
J
Alberts
David S
DS
Hamilton
Stanley R
SR
Issa
Jean-Pierre J
JP
D014408:Biomarkers, Tumor / Q000235:genetics*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology* / Q000473:pathology; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D012307:Risk Factors; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA; D013447:Sulfites; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D018631:ras Proteins
D014408:Biomarkers, Tumor; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D013447:Sulfites; D016159:Tumor Suppressor Protein p53; D019853:O(6)-Methylguanine-DNA Methyltransferase; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; C042345:hydrogen sulfite