Table 3. Blood-based prognostic biomarkers of GC.

Biosources		Biomarkers	No. of patients with GC	Methods	Clinical significance	Reference
Cellular components
	CTCs	>5 CTCs/7.5 mL	65	OBP-401	Poor OS	Ito et al. (2016) [88]
		≥2 CTCs/7.5 mL	106	CellSearch	Poor PFS and OS	Pernot et al. (2017) [89]
		>3 CTCs/7.5 mL	59	CellSearch, CTC-Biopsy system	Poor PFS and OS	Ning et al. (2021) [90]
		CD44+ CTCs	228	Immunofluorescent double staining	Poor OS	Szczepanik et al. (2019) [91]
		CSV+PD-1+ CTCs	70	Microbead selection method	Poor OS	Liu et al. (2020) [92]
		TWIST+ CTCs	31	Centrifugal microfluidic system	Poor OS	Jhi et al. (2021) [93]
	PBMCs	High CD3+CD8+ T-cells, low CD4+CD25+Foxp3+ Tregs	105	FACS	Increased OS	He et al. (2017) [94]
		TIM-3+CD8+ T-cells	47	FACS	Increased OS	Ma et al. (2023) [95]
		Early increase in PD-1+CD8+ T-cells after chemotherapy	68	FACS	Increased OS	Shin et al. (2023) [96]
Acellular components
	cfDNAs	cfDNA level	277	TaqMan qPCR	Peritoneal recurrence and poor OS	Fang et al. (2016) [97]
		Pre-surgical low methylation levels of LINE-1	99	HELP	Poor RFS and OS	Ko et al. (2021) [82]
		Methylation of RASSF1A, SOX17 and Wif-1	70	Methylation-specific PCR	Poor PFS and OS	Karamitrousis et al. (2021) [98]
	ctDNAs	ctDNA level	277	TaqMan qPCR (68 mutations in 8 genes)	Peritoneal recurrence and poor OS	Fang et al. (2016) [97]
		ctDNA level	35 (13 palliative)	Targeted NGS	Poor OS	Openshaw et al. (2020) [86]
		TP53 mutation and MET amplification	23	Multigene NGS-panel technology	Poor OS	Li et al. (2021) [99]
		SFRP2 hypermethylation	148	Methylation-specific dPCR	Poor PFS and OS	Yan et al. (2021) [100]
	miRNAs	High miR-23b level	138	qRT-PCR	Poor clinical outcome	Zhuang et al. (2016) [33]
		Low miR-212 level	110	qRT-PCR	Poor OS	Shao et al. (2020) [40]
		Low miR-148a level	132	qRT-PCR	Poor OS	Komatsu et al. (2021) [101]
	Exosomal lncRNAs	High lncRNA-HOTTIP level	126	qRT-PCR	Poor OS	Zhao et al. (2018) [69]
	Exosomal circRNAs	High hsa_circ_0015286 level	60	ExoQuick, TEM/NTA, qRT-PCR	Poor OS	Zheng et al. (2022) [74]

GC = gastric cancer; CTC = circulating tumor cell; OS = overall survival; PFS = progression-free survival; CD = cluster of differentiation; PD-1 = programmed cell death-1; PBMC = peripheral blood mononuclear cell; FACS = fluorescence-activated cell sorting; TIM-3 = T-cell immunoglobulin and mucin-domain containing-3; cfDNA = cell-free DNA; qPCR = quantitative polymerase chain reaction; HELP = HpaII tiny fragment enrichment by ligation-mediated polymerase chain reaction; RFS = relapse-free survival; NGS = next-generation sequencing; dPCR = digital polymerase chain reaction; miRNA = microRNA; qRT-PCR = quantitative reverse transcription polymerase chain reaction; lncRNA = long non-coding RNA; circRNA = circular RNA; TEM = transmission electron microscopy; NTA = nanoparticle tracking analysis.