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A tailored approach to BRAF and MLH1 methylation testing in a universal screening program for Lynch syndrome.

一种定制用于Lynch综合征普遍筛查方案中BRAF和MLH1甲基化检测的方法

Adar T,Rodgers LH,Shannon KM,Yoshida M,Ma T,Mattia A,Lauwers GY,Iafrate AJ,Chung DC
阅读:1275 Modern PathologyMar 2017; 30 (3): 316 - 469:440-447 

Abstract

To determine the correlation between BRAF genotype and MLH1 promoter methylation in a screening program for Lynch syndrome (LS), a universal screening program for LS was established in two medical centers. Tumors with abnormal MLH1 staining were evaluated for both BRAF V600E genotype and MLH1 promoter methylation. Tumors positive for both were considered sporadic, and genetic testing was recommended for all others. A total 1011 colorectal cancer cases were screened for Lynch syndrome, and 148 (14.6%) exhibited absent MLH1 immunostaining. Both BRAF and MLH1 methylation testing were completed in 126 cases. Concordant results (both positive or both negative) were obtained in 86 (68.3%) and 16 (12.7%) cases, respectively, with 81% concordance overall. The positive and negative predictive values for a BRAF mutation in predicting MLH1 promoter methylation were 98.9% and 41%, respectively, and the negative predictive value fell to 15% in patients ≥70 years old. Using BRAF genotyping as a sole test to evaluate cases with absent MLH1 staining would have increased referral rates for genetic testing by 2.3-fold compared with MLH1 methylation testing alone (31% vs 13.5%, respectively, P<0.01). However, a hybrid approach that reserves MLH1 methylation testing for BRAF wild-type cases only would significantly decrease the number of methylation assays performed and reduce the referral rate for genetic testing to 12.7%. A BRAF mutation has an excellent positive predictive value but poor negative predictive value in predicting MLH1 promoter methylation. A hybrid use of these tests may reduce the number of low-risk patients referred to genetic counseling and facilitate wider implementation of Lynch syndrome screening programs.

摘要

为了确定Lynch综合征(LS)筛查方案中BRAF基因型和MLH1启动子甲基化之间的相关性,在两个医疗中心制定了LS的普遍筛查方案。对具有异常MLH1染色的肿瘤中BRAF V600E基因型和MLH1启动子甲基化进行了评价。两者均阳性的肿瘤被认为是散发性的,其他所有情况均推荐进行基因检测。共1011例结直肠癌患者接受了Lynch综合征筛查,148(14.6%)例病例缺乏MLH1免疫染色。126例患者完成了BRAF和MLH1基因甲基化检测,得到一致性结果(均阳性或均阴性)的病例分别为86例(68.3%)和16例(12.7%),总的一致性为81%。BRAF突变预测MLH1启动子甲基化的阳性和阴性预测值分别为98.9%和41%,患者≥70岁时阴性预测值下降到15%。较之于单独的MLH1甲基化检测,使用BRAF基因型作为评价MLH1染色缺失患者的唯一检测,将增加基因检测的转诊率2.3倍(两者的比率分别为31% 和 13.5%,P<0.01)。然而,仅对BRAF野生型病例保留MLH1甲基化检测的混合性方法将会显著降低进行甲基化检测的次数并降低基因检测的转诊率到12.7%。BRAF基因突变在预测MLH1启动子甲基化方面具有良好的阳性预测值,但阴性预测值较差。这些测试的联合使用可能会缩减低风险患者的遗传咨询数量并促进Lynch综合征筛查方案的进一步推广。

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