Circulating tumor DNA (ctDNA) has emerged as a powerful tool for liquid biopsy (LB) to guide personalized treatment decisions in oncology. Effective clinical application requires well-defined ctDNA thresholds to detect residual disease and monitor tumor burden dynamics during therapy. In this study, we evaluated the clinical validity of the limit of blank (LOB) and limit of quantification (LOQ) for assays targeting key somatic mutations in colorectal cancer (CRC), including BRAF p.V600E and KRAS p.G12/p.G13, across 212 plasma samples. Using the LOB to define ctDNA positivity, we observed strong agreement with evidence of metastasis or disease recurrence. Similarly, applying the LOQ as a threshold for quantitative ctDNA changes reliably reflected tumor burden fluctuations during chemotherapy and throughout disease progression. Comparison with conventional markers, such as carcinoembryonic antigen (CEA) and circulating free DNA (cfDNA) levels, demonstrated that ctDNA-based LB provides superior accuracy in detecting residual disease and predicting tumor burden changes. These findings highlight the potential of validated ctDNA assays to enhance monitoring and clinical management of CRC patients.
