Utility of circulating tumor DNA in the clinical management of patients with <i>BRAF<sup>V600E</sup></i> metastatic colorectal cancer.
Authors: Van K. Morris, Kanwal Pratap Singh Raghav, Arvind Dasari, Michael J. Overman, Bryan K. Kee, Benny Johnson, Christine Megerdichian Parseghian, John Paul Y.C. Shen, Ryan Huey, Victoria M. Raymond, Dzifa Yawa Duose, Rajyalakshmi Luthra, David S. Hong, Filip Janku, Scott Kopetz
Journal: Journal of Clinical Oncology (2021)

119 Background: Molecular profiling is critical for oncologists in personalizing treatment decisions for patients (pts) with metastatic colorectal cancer (mCRC). In contrast to archival tumor tissue specimens classically used profiling, sequencing of circulating tumor DNA (ctDNA) is more sensitive at quantifying low mutation allele frequencies and characterize “real time” tumor biology. We assessed the relationship between detection of BRAF V600E mutations in ctDNA and the clinical management of pts with mCRC. Methods: We retrospectively analyzed mCRC patients evaluated at MD Anderson Cancer Center with BRAF V600E mutations on ctDNA. ctDNA was isolated and sequenced for somatic mutations using a 70-gene next-generation sequencing assay (MD Anderson/GuardantHealth LB70 panel). Variant allele frequency (VAF) was characterized as the ratio of mutant reads: total reads for a given gene. BRAF V600E mutations were classified as “clonal” if the relative VAF (rVAF) exceeded 50% of the maximum VAF. “Major” and “minor” subclonal mutations were called for a rVAF of 10-50% and &lt; 10%, respectively. Associations between BRAF V600E clonality and treatment decision were performed using a Fisher’s exact test. Survival outcomes were estimated using the Kaplan-Meier method. Results: 64 patients with mCRC had a BRAF V600E mutation detected in ctDNA. Concordance between tissue and ctDNA for BRAF V600E mutation was occurred in 44/55 (80%) patients with evaluable tumor specimen. There were 9 patients with BRAF V600E mutations identified in the absence of evaluable tumor tissue. Median VAF for BRAF V600E in the ctDNA was 3.6% (interquartile range, 0.50 – 17%). The majority of patients had a clonal BRAF V600E mutation (50/64, 78%). There were 3 (5%) and 11 (17%) patients with major subclonal and minor subclonal BRAF V600E mutations, respectively. Among patients with minor subclonal BRAF V600E mutations, 91% (10/11) had developed resistance to anti-EGFR therapies for management of RAS wild -type mCRC. Discordance between tissue and ctDNA BRAF V600E status was associated with minor subclones (odds ratio (OR) 56, p &lt; .0001). Clonal BRAF V600E mutations in the ctDNA were associated with a higher likelihood for treatment with BRAF targeted therapies (OR 5.8, p = .008). Median progression-free survival among 37 evaluable patients was 6.4 months. Conclusions: Reported VAF in the ctDNA served to stratify BRAF V600E according to relative clonality. Lower VAF was linked to acquired resistance to anti-EGFR therapies, whereas higher VAF was associated with receipt of matched targeted therapies for BRAF V600E mCRC. ctDNA technologies for identifying BRAF V600E mutations are feasible and informative for conducting relevant molecular profiling for patients with mCRC.