Fig. 1

Basic introduction of the liquid biopsy approaches and applications of CTCs as liquid biopsy. a Liquid biopsy approaches involve peripheral blood, precardial effusion, stool, urine, ascites, pleural effusion, saliva and cerebrospinal fluid. Moreover, peripheral blood biopsy include isolation of circulating tumor cells(CTCs), circulating tumor DNA (ctDNA), circulating tumor RNA(ctRNA) and exosomes. b Applications of CTCs as liquid biopsy in early diagnosis, prognosis prediction, and disease monitoring, molecular phenotyping, therapy response evaluation