BRAF mutation testing of MSI CRCs in Lynch syndrome diagnostics: performance and efficiency according to patient`s age

Background and aims: BRAF V600E mutations have been reported to be associated with sporadic microsatellite-unstable (MSI) colorectal cancer (CRC), while rarely detected in CRCs of Lynch syndrome (LS) patients. Therefore, current international diagnostic guidelines recommend somatic BRAF mutation testing in MLH1-deficient MSI CRC patients to exclude LS. As sporadic BRAF-mutant MSI CRC is a disease of the elderly, while LS-associated CRC usually occurs at younger age, we hypothesized that the efficacy of BRAF testing in LS diagnostics may be age-dependent. Methods: We systematically compared the prevalence of BRAF V600E mutations in LS-associated CRCs and MSI CRCs from population-based cohorts in different age groups as available from published studies, databases, and population-based patient cohorts. Cost calculations and sensitivity analysis of the BRAF testing for exclusion of LS was performed. Results: Among 969 MSI CRCs from LS mutation carriers from the literature and German HNPCC Consortium, 15 (1.6%, 95% CI: 0.9-2.6%) harbored BRAF mutations. 6/7 LS patients with BRAF-mutant CRC and reported age were 60 years. In MSI CRC patients <50, BRAF mutations were detected only in 0.6% (2/339), and the inclusion of BRAF testing led to increased costs and higher risk of missing LS patients (1.2%) compared to other age groups. Conclusion: BRAF testing in patients