Liquid Biopsy and Circulating Tumor DNA: Applications in Early Detection, Monitoring, and Minimal Residual Disease

Liquid biopsy, particularly through the detection and analysis of circulating tumor DNA (ctDNA), has emerged as a minimally invasive tool with broad clinical potential in oncology. This chapter reviews the biological basis and technical platforms underlying ctDNA analysis, evaluates clinical applications ranging from early cancer detection and real-time treatment monitoring to assessment of minimal residual disease and clonal evolution, and discusses the current limitations and unresolved questions that must be addressed before widespread clinical implementation.