散发性结直肠癌中的MGMT启动子甲基化与场缺陷

MGMT promoter methylation and field defect in sporadic colorectal cancer.

作者信息

Shen Lanlan, Kondo Yutaka, Rosner Gary L, Xiao Lianchun, Hernandez Natalie Supunpong, Vilaythong Jill, Houlihan P Scott, Krouse Robert S, Prasad Anil R, Einspahr Janine G, Buckmeier Julie, Alberts David S, Hamilton Stanley R, Issa Jean-Pierre J

机构信息

Department of Leukemia, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.

出版信息

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

DOI:10.1093/jnci/dji275

PMID:16174854

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.

摘要

背景

散发性结直肠癌通常起源于一个细胞区域，该区域具有尚未在分子水平上明确界定的“场缺陷”。DNA甲基化已被提出作为这种场缺陷的候选介质。DNA修复基因O6-甲基鸟嘌呤-DNA甲基转移酶（MGMT）在结直肠癌中经常发生甲基化。我们假设MGMT甲基化可能是结肠黏膜场癌化的介质之一。

方法

我们采用三种不同的亚硫酸氢盐技术，研究了95例结直肠癌患者肿瘤、癌旁黏膜和非癌旁黏膜以及33例无癌症证据受试者的结肠黏膜中MGMT启动子甲基化情况。统计检验采用双侧检验。

结果

46%的肿瘤中存在MGMT启动子甲基化。癌症具有MGMT启动子甲基化的患者，其明显正常的癌旁黏膜中也存在大量MGMT启动子甲基化。通过定量分析，在癌旁肿瘤中具有MGMT启动子甲基化的正常样本中，50%（22/44；95%置信区间[CI]=34%至65%）检测到这种甲基化；在癌旁肿瘤中无MGMT甲基化的样本中，6%（3/51；95%CI=1%至16%）检测到；在对照样本中，12%（4/33；95%CI=3%至28%）检测到（后两组与第一组比较，P<.001）。使用更灵敏的检测方法，这些样本中分别有94%、34%和27%检测到MGMT甲基化（P<.001）。在结肠癌患者大体正常的结肠黏膜中，13例中有10例在距肿瘤10厘米处检测到甲基化。具有MGMT启动子甲基化的肿瘤，其KRAS癌基因中G-to-A突变率高于无MGMT启动子甲基化的肿瘤（10/42对3/46，P=.03）。使用灵敏的KRAS突变等位基因特异性扩增检测方法，我们还发现在可检测到MGMT甲基化的结直肠黏膜中，12%（3/25；95%CI=2.5%至31%）存在KRAS突变，在无MGMT甲基化的结直肠黏膜中，3%（2/64；95%CI=0.4%至11%）存在KRAS突变（P=.13）。