Diagnostic strategies towards clinical implementation of liquid biopsy RAS/BRAF circulating tumor DNA analyses in patients with metastatic colorectal cancer.

Detection of KRAS, NRAS and BRAF mutations in tumor tissue is currently used to predict resistance to treatment with anti-EGFR antibodies of patients with metastatic colorectal cancer (mCRC). Liquid biopsies are minimally invasive and cell-free circulating tumor DNA (ctDNA) mutation analyses may better represent tumor heterogeneity. This study examined the incorporation of liquid biopsy RAS/BRAF ctDNA analyses into diagnostic strategies to determine mCRC patient eligibility for anti-EGFR therapy. Tumor tissue and liquid biopsies were collected from 100 mCRC patients with liver-only metastases who participated in a multi-center prospective clinical trial. We compared three diagnostic strategies incorporating droplet digital PCR ctDNA analyses to routine tumor tissue RAS/BRAF mutation profiling using decision tree analyses. Tissue DNA mutations in KRAS, NRAS and BRAF were present in 54%, 0% and 3% of mCRC patients, respectively. A 93% concordance was observed between tissue DNA and liquid biopsy ctDNA mutations. The proportion of patients with RAS/BRAF alterations increased from 57% to 60% for diagnostic strategies that combined tissue and liquid biopsy mutation analyses. Consecutive RAS/BRAF ctDNA analysis followed by tissue DNA analysis in case of a liquid biopsy-negative result appeared to be the most optimal diagnostic strategy to comprehensively determine eligibility for anti-EGFR therapy in a cost-saving manner. These results highlight the potential clinical utility of liquid biopsies for detecting primary resistance to anti-EGFR targeted therapies.