Quantitative ctDNA Profiling of RAS Mutations as a Prognostic Biomarker in Metastatic Colorectal Cancer

Background: Circulating tumor DNA (ctDNA) analysis offers a non-invasive approach to molecular profiling. While RAS mutations are well-established predictive biomarkers in metastatic colorectal cancer (mCRC), the prognostic value of their variant allele fre-quency (VAF) remains unclear. Methods: We retrospectively analyzed individual patient data with mCRC who un-derwent ctDNA testing using the FoundationOne® Liquid CDx assay. The primary objective was to determine the optimal RAS VAF cutoff for overall survival (OS) prog-nostication. Results: Between November 2020 and July 2024, 282 patients were enrolled. Among 265 eligible patients, 134 (50.6%) were ctRAS mutant, 25 (9.4%) ctBRAF V600E mutant, and 106 (40.0%) were ctRAS/BRAF wild-type. A RAS VAF threshold of 5% yielded the highest prognostic discrimination for OS (HR = 2.41; 95% CI: 1.65–3.55; p < 0.0001; C-index = 0.601). ctRAS-high mutant tumors (VAF ≥ 5%) were associated with syn-chronous metastatic disease, multiple metastatic sites, higher blood tumor mutational burden, and elevated tumor fraction. ctRAS-low mutant tumors (VAF < 5%) were more frequently metachronous, presented with a single metastatic site, and liver involve-ment. Conclusion: High RAS VAF in ctDNA is a strong and independent prognostic marker for OS in mCRC. Quantitative ctDNA profiling may enhance risk stratification and guide personalized management strategies.