吸烟、CpG岛甲基化表型与结肠癌中V600E BRAF突变的关联

Association of smoking, CpG island methylator phenotype, and V600E BRAF mutations in colon cancer.

作者信息

Samowitz Wade S, Albertsen Hans, Sweeney Carol, Herrick Jennifer, Caan Bette J, Anderson Kristin E, Wolff Roger K, Slattery Martha L

机构信息

Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, UT 84132, USA.

出版信息

J Natl Cancer Inst. 2006 Dec 6;98(23):1731-8. doi: 10.1093/jnci/djj468.

DOI:10.1093/jnci/djj468

PMID:17148775

Abstract

BACKGROUND

Cigarette smoking has been associated with microsatellite instability in sporadic colon cancer. Most microsatellite-unstable colon cancers have widespread methylation of CpG islands (i.e., the CpG island methylator phenotype [CIMP]), and many of these tumors harbor the V600E BRAF mutation. We investigated whether the association between smoking and all colon cancers could be explained through induction of CIMP and/or BRAF mutations.

METHODS

We evaluated 1315 case patients with colon cancer and 2392 control subjects in a population-based study. Demographic information, including smoking history, was obtained in an interview. Microsatellite instability was determined primarily by evaluation of the mononucleotide repeat BAT-26. CIMP was determined by sodium bisulfite modification of DNA followed by methylation-specific polymerase chain reaction amplification of CpG islands in hMLH1, p16, and MINTS1, -2, and -31. Tumors were scored as CIMP high (i.e., > or = 2 CpG islands methylated) or CIMP low (i.e., < 2 CpG islands methylated). BRAF V600E mutations were identified by sequencing. Logistic regression was used to quantify relationships among smoking, CIMP, and BRAF. All statistical tests were two-sided.

RESULTS

Heavy smoking (i.e., > 20 cigarettes per day), compared with nonsmoking, was associated with an increased risk of CIMP-high colon cancer (odds ratio [OR] = 2.06, 95% confidence interval [CI] = 1.43 to 2.97) and also with BRAF V600E mutations (OR = 3.16, 95% CI = 1.80 to 5.54). The association between cigarette smoking and the risk of colon cancer was limited to the minority of tumors that were CIMP high and BRAF wild type or CIMP high and BRAF mutated (for heavy smokers, OR = 1.91, 95% CI = 1.23 to 2.97, and OR = 2.85, 95% CI = 1.53 to 5.29, respectively). All relationships above showed a statistically significant relationship to amount smoked (P(trend) < .001 for all, except that relationship with tumors that were CIMP high and BRAF wild type, for which P(trend) = .008) and were independent of microsatellite instability.

CONCLUSIONS

Previously identified associations between smoking and colon cancer, whether microsatellite unstable or stable, appear to be explained by the association of smoking with CIMP and BRAF mutations.

摘要

背景

吸烟与散发性结肠癌中的微卫星不稳定性有关。大多数微卫星不稳定的结肠癌具有广泛的CpG岛甲基化（即CpG岛甲基化表型 [CIMP]），并且这些肿瘤中的许多都存在V600E BRAF突变。我们研究了吸烟与所有结肠癌之间的关联是否可以通过诱导CIMP和/或BRAF突变来解释。

方法

在一项基于人群的研究中，我们评估了1315例结肠癌患者和2392名对照者。通过访谈获取包括吸烟史在内的人口统计学信息。微卫星不稳定性主要通过评估单核苷酸重复序列BAT-26来确定。CIMP通过DNA的亚硫酸氢盐修饰，随后对hMLH1、p16以及MINTS1、-2和-31中的CpG岛进行甲基化特异性聚合酶链反应扩增来确定。肿瘤被评定为CIMP高（即≥2个CpG岛甲基化）或CIMP低（即<2个CpG岛甲基化）。通过测序鉴定BRAF V600E突变。使用逻辑回归来量化吸烟、CIMP和BRAF之间的关系。所有统计检验均为双侧检验。

结果

与不吸烟相比，重度吸烟（即每天>20支香烟）与CIMP高的结肠癌风险增加相关（比值比 [OR]=2.06，95%置信区间 [CI]=1.43至2.97），也与BRAF V600E突变相关（OR=3.16，95%CI=1.80至5.54）。吸烟与结肠癌风险之间的关联仅限于少数CIMP高且BRAF野生型或CIMP高且BRAF突变的肿瘤（对于重度吸烟者，OR分别为1.91，95%CI=1.23至2.97，以及OR=2.85，95%CI=1.53至5.29）。上述所有关系均显示出与吸烟量存在统计学显著关系（除了与CIMP高且BRAF野生型肿瘤的关系，其P趋势=0.008，其他所有关系的P趋势<0.001），并且独立于微卫星不稳定性。