1145P - Analysis of BRAF V600E mutation status – concordance of results from circulating tumor DNA and tissue-based testing and impact on prediction of the clinical course in patients undergoing BRAFi therapy

Abstract

The current standard for determining eligibility of patients with metastatic melanoma for BRAF-targeted therapy is the tissue-based testing of BRAF mutations. As patients are rarely re-biopsied, the detection in blood in real-time might be advantageous reflecting the current mutational status of the patient's disease. Furthermore, metastatic melanoma lacks clinically efficient biomarkers. Here, genetic testing in plasma may represent a useful noninvasive biomarker for monitoring BRAF therapy. Blood samples from melanoma patients in two independent studies were subjected to plasma testing using the OncoBEAMTM BRAF V600E assay and tissue-based analysis using Sanger sequencing. In the first study, the tissue-based BRAF mutation status was compared with matched plasma samples from 74 patients diagnosed with progressive metastatic melanoma being either treatment-naïve or undergoing BRAFi therapy. In the second study, the mutational status in tissue and plasma samples from 131 patients of melanoma stage III or IV was compared in follow-up. Overall, results from BRAF plasma testing revealed a high degree of concordance with tissue testing in both studies with 89.2% (study 1) and 94% (study 2), respectively. In the second study 2 of 3 patients with negative OncoBEAM results in plasma, but with positive test in tumor tissue, did not respond to BRAFi therapy potentially due to a false positive result. 5 of 10 patients originally classified BRAF-negative in tumor, tested BRAF mutation-positive in plasma. In these cases, secondary malignancies were found to be responsible. Importantly, dynamic changes of BRAF mutant ctDNA over time correlated with the clinical course and response to treatment. Positivity of BRAF plasma testing was significantly earlier detectable than relapse using radio-imaging. Blood-based testing favorably compares with standard-of-care tissue-based BRAF mutation testing. Importantly, blood-based BRAF testing may be used to predict response to treatment and resistance prior to radio-imaging under BRAFi therapy thereby allowing for an improved treatment management.