Precision medicine for cancer patients aims to adopt the most suitable treatment options during diagnosis and treatment of individuals.Detecting circulating tumor cell (CTC) or circulating tumor DNA (ctDNA) in plasma or serum could serve as liquid biopsy,which would be useful for numerous diagnostic applications.Liquid biopsies can help clinicians screen and detect cancer early,stratify patients to the most suitable treatment and real-time monitoring of treatment response and resistance mechanisms in the tumor,evaluate the risk for metastatic relapse,and estimate prognosis.We summarized the advantages and disadvantages of tissue and liquid biopsies.We also further compared and analyzed the advantages and limitations of detecting CTCs,ctDNAs,and exosomes.Furthermore,we reviewed the literature related with the application of serum or plasma CTCs,ctDNAs,and exosomes for diagnosis and prognosis of cancer.We also analyzed their opportunities and challenges as future biomarkers.In the future,liquid biopsies could be used to guide cancer treatment.They could also provide the ideal scheme to personalize treatment in precision medicine.