A New Era of Salvage-Line Treatment for Metastatic Colorectal Cancer: The Role and Clinical Significance of Circulating Tumor DNA

The emergence of novel cytotoxic agents, multikinase inhibitors, and various antibody-based therapies has significantly expanded salvage therapy options for metastatic colorectal cancer (mCRC). Consequently, establishing the optimal treatment sequence for patients has become a formidable clinical challenge. Emerging evidence highlights the value of comprehensive biomarker assessment, particularly longitudinal monitoring of circulating tumor DNA (ctDNA), to capture dynamic molecular changes during treatment. Liquid biopsy-based technologies now enable real-time tracking of molecular alterations, supporting truly personalized therapeutic decision-making. Furthermore, prior treatment exposure and residual toxicities must be carefully considered to balance efficacy, safety, and quality of life. This review provides a comprehensive overview of the current salvage-line landscape for mCRC, discusses the clinical utility of ctDNA as a predictive and prognostic tool, and proposes integrated strategies to optimize therapeutic outcomes in the evolving era of precision medicine.