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

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.

Methylation and expression analysis of mismatch repair genes in extramammary Paget's disease

“…31 But in Lynch syndrome-associated tumours (positive for germline MMR genes mutations), MLH1 methylation is a rare event that sensitive and specific detection of it could be important to distinguish whether the tumour samples are from Lynch syndrome or other cancers. 32,33 By contrast, recent evidence indicates MSH2 methylation mainly occurs on a somatic basis in the tumour tissues with Lynch syndrome. 34 Interestingly, our results also showed a high detection rate of MSH2 methylation in EMPD tumour samples but not in adjacent normal tissues.…”

Distinct clinical phenotype and genetic testing strategy for Lynch syndrome in China based on a large colorectal cancer cohort

“…These findings highlight the importance of considering the family history of LSRC in deciding to exclude sporadic MLH1‐deficient CRCs by MLH1 promoter methylation to avoid inadvertently missing LS carriers. Collectively, we assume that in clinical practice a hybrid testing of BRAF mutation and MLH1 promoter methylation should be adopted especially for Chinese MLH1‐deficient CRCs to reduce unnecessary genetic testing …”

“…Collectively, we assume that in clinical practice a hybrid testing of BRAF mutation and MLH1 promoter methylation should be adopted especially for Chinese MLH1-deficient CRCs to reduce unnecessary genetic testing. 29 Analysis of LGRs in LS screening using a next-generation sequencing bioinformatics workflow is not well established. 30 Currently, MLPA has been adopted as a simple, highly specific and sensitive technique for detecting LGRs in MMR genes.…”

Clinical and molecular characterisation of hereditary and sporadic metastatic colorectal cancers harbouring microsatellite instability/DNA mismatch repair deficiency

“…MMR genes germline mutation cannot always be detected in LS and the definition of sporadic MSI/dMMR CRCs and CRCs presumed to be LS-related (i.e. Lynch-like) has evolved over time, from clinical criteria to a tailored approach with BRAF and MLH1 methylation testing for CRCs showing a loss of MLH1 expression [2][3][4][5].…”