Liquid Biopsy: Circulating Biomarkers and Their Pathological Significance

This chapter reviews the scientific principles and clinical utility of liquid biopsy, encompassing circulating tumor DNA, cell-free RNA, circulating tumor cells, and extracellular vesicles as sources of actionable pathological information. It synthesizes the growing body of evidence supporting the use of liquid biopsy for early cancer detection, real-time monitoring of treatment response, and identification of resistance mechanisms, while critically evaluating the technical and analytical limitations that currently constrain broader clinical implementation. The role of liquid biopsy in longitudinal disease monitoring and its integration with tissue-based pathological diagnosis are also discussed.