Precision medicine and personalized medicine are based on the development of biomarkers, and liquid biopsy has been reported to be able to detect biomarkers that carry information on tumor development and progression. Compared with traditional ‘solid biopsy’, which cannot always be performed to determine tumor dynamics, liquid biopsy has notable advantages in that it is a noninvasive modality that can provide diagnostic and prognostic information prior to treatment, during treatment and during progression. Here, researchers describe the source, characteristics, technology for detection and current situation of circulating tumor cells, circulating free DNA and exosomes used for diagnosis, recurrence monitoring, prognosis assessment and medication planning.
Schematic of the origin of cfDNA, CTCs and exosomes in the blood. cfDNA can be released from healthy, inflamed or tumor tissue undergoing apoptosis or necrosis. Tumor cells can also actively intrude the circulatory system or can be pushed into the bloodstream by external forces, such as tumor growth or mechanical forces during surgical operation. These tumor cells can be shielded by platelets. Moreover, circulating exosomes can be generated by many cell types, including tumor cells, normal cells, and blood cells (even platelets). Abbreviations: cfDNA, cell-free DNA; CTCs, circulating tumor cells.