Table 1.

Summary of characteristics of different blood-based biomarkers. The different advantages and disadvantages of the blood-based biomarkers, that favor or disfavor their use in clinical settings, are shown in the table. BEAMing: beads, emulsions, amplification and magnetics; cfDNA: circulating cell-free DNA; bTMB: blood tumor mutational burden; EpCAM: epithelial cell adhesion molecule; miRNA: microRNA; NGS: next-generation sequencing; NSCLC: non-small cell lung cancer; PD-L1: programmed death-ligand 1; TCR: T cell repertoire.

Type	Isolation Technique	Advantages	Disadvantages	Promising Biomarker	References
Cell-free DNA	Magnetic beads or spin column based	- Easy and well-established isolation procedures - Allows real-time monitoring	- Short half-life: 16 min–2.5 h - Not stable in circulation - Long turn-around time NGS based tests - Sensitive detection methods required	bTMB and levels of cfDNA for cancer diagnosis and treatment evaluation	[17,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53]
Circulating tumor cells	Antigen-dependent (e.g., EpCAM) or size and deformability based method	- Provides transcriptomic, genomic and proteomic information	- Short half-life: 1–2.4 h - Not stable in circulation	PD-L1 analysis status to predict response on treatment	[15,25,54,55,56,57,58,59,60,61,62,63,64]
		- Intact viable cells	- Low abundance in NSCLC
			- Isolation procedures requires high expertise and dedicated equipment
Exosomes	Based on physical or biological properties of exosomes, immune-mediated isolation, sucrose gradient method, ultra-centrifugation	- Provides information about tumor’s biologic profile, growth rate, metastatic capacity and drug resistance - Abundant	- Isolation can be time-consuming and can alter exosome structure - Difficult to detect due to small size	Exosomal PD-L1 status to predict response on therapy	[25,65,66,67,68,69,70,71,72,73,74]
Epigenetics and miRNA	cfDNA isolation followed by methylation specific PCR or BEAMing	- Methylation makes cfDNA more stable - Allows real-time monitoring	- Sensitive detection methods required	Methylation status of genes (signature) for cancer diagnosis and treatment evaluation	[75,76,77,78,79,80,81,82,83,84,85,86,87]
T cell repertoire	Density centrifugation followed by flowcytometry	- Easy isolation - Intact viable cells	- Clustering of functionally different clones causing false positive results	The frequency, diversity and clonality of TCRs for cancer diagnosis and treatment evaluation	[41,57,88,89,90,91,92]