Table 1.

Soluble PD-1 expression levels in different cancers and their correlation with disease prognosis and efficacy prediction.

Cancer type	Patients number	Treatment	Principal findings	Reference
NSCLC	38	Erlotinib	34% of patients showed an increase in sPD-1 during erlotinib treatment; Increased sPD-1 during treatment was associated with prolonged PFS (adjusted HR 0.32, p = 0.013) and OS (adjusted HR 0.33, p = 0.006).	(78)
NPC	77	IMRT	IMRT could increase the expression of sPD-1; The expression level of sPD-1 in TNM I/II patients was significantly higher than that in III/IV patients; Patients with high sPD-1 had longer survival than those with low sPD-1.	(79)
NSCLC	87	Nivolumab	After two cycles of nivolumab, an increased or stable sPD-1 level independently correlated with longer PFS (HR 0.49, 95%CI (0.30-0.80), p = 0.004) and OS (HR 0.39, 95%CI (0.21-0.71), p = 0.002).	(28)
HCC	120	Radical resection	sPD-1 was a favorable independent prognostic factor (DFS, HR 0.32, 95%CI (0.14-0.74), p = 0.007; OS, HR 0.54, 95%CI (0.30-0.98), p = 0.044).	(53)
Advanced rectal cancer	117	CRT	High sPD-1 before and after CRT was significantly associated with longer distance of the tumor from the anal verge.	(80)
PDAC	32	/	Plasma level threshold that correlates with less than six months survival was established for sPD-1 (>8.6 ng/ml).	(81)
DLBCL	121	Immunochemotherapy	The relative risk of death was 2.9-fold (95%CI (1.12-7.75), p = 0.028) and the risk of progression was 2.8-fold (95%CI (1.16-6.56), p = 0.021) in patients with high pretreatment sPD-1 levels	(82)

PD-1, soluble programmed death protein 1; NSCLC, non-small cell lung cancer; PFS, progression-free survival; HR, hazard ratio; OS, overall survival; NPC, nasopharyngeal carcinoma; IMRT, intensity-modulated radiation therapy; CI, confidence interval; HCC, hepatocellular carcinoma; DFS, disease-free survival; CRT, chemoradiotherapy; PDAC, pancreatic ductal adenocarcinoma; DLBCL, diffuse large B-cell lymphoma.