Table 1.

Biomarkers for cancer immunotherapy.

Sample	Biomarker	Clinical Significance
Tumor Tissue	PD-L1	Increased expression in tumor cells is associated with a positive clinical response to anti-PD-1/PD-L1 antibodies [16,21,22,23,24,25].
	TMB	High TMB is associated with an improved response to ICIs [26,27].
	MMR	MMR deficiency, regardless of tumor types, correlates with a clinical response to pembrolizumab [28,29,30,31,32,33].
	TIL	The presence of tumor-infiltrating CD8+ T cells is associated with a better prognosis [34,35,36,37,38,39].
	Tregs/ MDSCs	The presence of tumor-infiltrating Tregs and MDSCs is associated with a poor prognosis [40,41,42,43,44,45,46].
Peripheral Blood	Neutrophils/leukocytes	Elevated NLR is associated with a poor response [7,47,48,49,50].
	Low % of lymphocytes	Patients with a lymphocyte count less than 15% should be excluded from immunotherapy [7].
	LDH	Elevated pretreatment levels are correlated with a worse OS [51,52,53,54,55,56,57,58,59].
	CRP	High level of CRP is associated with an increased risk of OS [60].
	miRNA	Expression of several miRNAs is associated with clinical outcomes [61,62].
	Tregs/ MDSCs	Decreased level of circulating Tregs and MDSCs after treatment correlated with improved prognosis [6,60,63].
	Ki-67 expression	Increased Ki-67 expression in PD1+ CD8+ T cells is associated with a good response [64,65].
Feces	Microbiome	The presence of Ruminococcaceae/Faecalibacterium in melanoma patients and Akkermansia muciniphila in NSCLC and RCC is associated with a clinical response to anti-PD-1 antibody [66,67].

PD-L1, programmed cell death-1 ligand 1; PD-1, programmed cell death receptor-1; TMB, tumor mutation burden; ICIs, immune checkpoint inhibitors; MMR, mismatch repair; TIL, tumor-infiltrating lymphocyte; Treg, regulatory T cells; MDSC, myeloid-derived suppressor cells; NLR, neutrophil-to-lymphocyte ratio; LDH, lactate dehydrogenase; OS, overall survival; CRP, C-reactive protein; miRNA, micro ribonucleic acid; NSCLC, non-small-cell lung carcinoma; RCC, renal cell cancer.