BRAF V600E Mutation Analysis Simplifies the Testing Algorithm for Lynch Syndrome
Ming Jin, Heather Hampel, Xiaoping Zhou, Lisa Schunemann, Martha M Yearsley, Wendy L Frankel. Ohio State University, Columbus, OH
Background: Lynch syndrome (LS), the most common inherited predisposition to colorectal cancer (CRC), is associated with germline mutations in DNA mismatch repair (MMR) genes. Immunohistochemistry (IHC) staining for MMR proteins is well established in CRCs to identify patients who are more likely to have LS and to help direct gene testing. Reflex testing for the BRAF-V600E mutation analysis has been suggested when the MLH1 and PMS2 proteins are absent, since BRAF mutations are not present in CRCs from patients with LS but are associated with sporadic CRCs due to MLH1 promoter hypermethylation. We evaluated our experience to determine the impact of adding reflex BRAF analysis following IHC staining.
Design: All newly diagnosed CRCs at our institution are screened by IHC stains for the MMR proteins (MLH1, MSH2, MSH6 or PMS2). Proteins exhibiting any convincing nuclear staining (greater than 1-5%) were considered present. Since 1/1/09, BRAF V600E mutation analysis has been performed for CRC with absence of MLH1 and PMS2 proteins. Mutation analysis was carried out on genomic DNA extracted from paraffin embedded tumor tissue by PCR amplification of BRAF exon 15 followed by direct sequencing. Those patients with BRAF mutation were not contacted since they were presumed not to have LS, while those without BRAF mutation were contacted for follow-up genetic counseling and testing.
Results: From 1/1/2009 to 7/10/2012, 90 of 412 (22%) CRCs screened had at least one MMR stain absent. Sixty-five (15.8%) had MLH1 and PMS2 absent and 25 (6.1%) had any other stain(s) absent. BRAF V600E mutation was found in 36 of 65 (55%) CRCs with absent MLH1 and PMS2 stains. Of all cases screened, 54 of 412 (13%) required follow-up after the addition of BRAF analysis compared to 90 who would have required follow-up without BRAF analysis. Therefore, the addition of BRAF analysis to the testing algorithm reduced the number of CRCs requiring follow-up genetic counseling by 40% (54 vs.90). Additional testing found that 4 patients with absent MLH1 and PMS2 and negative BRAF mutation had MLH1 hypermethylation.
Conclusions: Routine IHC staining of MMR proteins on newly diagnosed CRCs is feasible and can be clinically implemented. Reflex BRAF mutation testing in cases with absence of MLH1 and PMS2 reduced the number of patient contacts and simplified the genetic testing for LS, likely leading to cost savings. It appears that MLH1 promoter methylation testing may be even more effective at reducing the number of cases that need follow-up genetic counseling and testing.
Monday, March 4, 2013 1:00 PM
Poster Session II # 121, Monday Afternoon