Liquid biopsies in colorectal cancer screening and diagnosis

Table 2 Comparison of components in liquid biopsy

	CTCs	ctDNA	TEPs	Exosomes	RNA
Detection methods	CellSearch system, immunomagnetic bead enrichment, membrane filtration method	dPCR, next-generation sequencing, methylation sequencing, ARMS-PCR	Supercritical centrifugation, size exclusion chromatography, immune affinity capture	Ultra-high speed centrifugation, SEC, commercial extraction kits, microfluidic technology	qRT-PCR, dPCR, transcriptome sequencing
Representative biomarkers	EpCAM, CK8/18/19; CD44, CD133, ALDH1	KRAS, NRAS, BRAF, TP53; SEPT9, SDC2, VIM; MSI/MMR status	EGFR, EpCAM; vesicle-associated miRNAs	CD9, CD63, CD81; miR-92a, EGFR	miRNA, circRNA, lncRNA
Advantages	Obtain comprehensive tumor cell information, directly reflecting phenotype, stemness, and metastatic potential	The detection technology is mature with high standardization and excellent sensitivity	Stability superior to free nucleic acids with stable content	Long blood half-life and high stability	High sensitivity with a wide range of biomarkers
Limitations	Low abundance in peripheral blood, platform variability, and complex biological characteristics such as EMT	Early CRC exhibits extremely low abundance	No unified gold standard for separation and purification	Lack of unified separation criteria makes purity control difficult	Free RNA is highly susceptible to degradation, requiring stringent sample processing protocols
Clinical evidence level	Moderate to high level of evidence	High-quality evidence	Limited clinical evidence	Preclinical translational phase	Moderate evidence
Study size and validation cohort	Prospective large cohort studies on early CRC are insufficient	Predominantly prospective cohort	Lack of multicenter prospective validation	Multicenter validation cohort scarcity	The multicenter independent validation cohort requires refinement

CTC: Circulating tumor cell; ctDNA: Circulating DNA; TEP: Tumor-educated platelet; dPCR: Digital polymerase chain reaction; ARMS-PCR: Amplification-refractory mutation system polymerase chain reaction; qRT-PCR: Quantitative reverse transcription polymerase chain reaction; SEC: Size exclusion chromatography; EpCAM: Epithelial cell adhesion molecule; ALDH1: Aldehyde dehydrogenase 1; MSI: Microsatellite instability; MMR: Mismatch repair; EGFR: Epidermal growth factor receptor; circRNA: Circular RNA; lncRNA: Long noncoding RNA; EMT: Epithelial mesenchymal transition; CRC: Colorectal cancer; miRNA: Micro RNA.