Table 2.

Hazard ratio for the association between IDO overexpression and solid tumors prognosis

Stratified analysis	Effect size	NO. of study	Cases	HR		Heterogeneity
				Pooled HR (95% CI)	P value	I2 (%)	p value
All studies
OS	OS	28	3457	1.92 (1.52–2.43)	< 0.001	81.1	< 0.001
TTP	TTP	14	1815	2.25 (1.58–3.22)	< 0.001	54.8	0.007
Study location
Asia	OS	16	2137	2.12 (1.54–2.92)	< 0.001	68.5	< 0.001
	TTP	9	1121	2.48 (1.74–3.55)	< 0.001	11.4	0.342
Other countries	OS	12	1320	1.66 (1.17–2.37)	0.005	82.2	< 0.001
	TTP	5	694	1.99 (1.32–2.98)	0.001	14.3	0.323
Detection method
IHC	OS	25	3180	1.86 (1.46–2.38)	< 0.001	81.3	< 0.001
	TTP	14	1815	2.25 (1.58–3.22)	< 0.001	54.8	0.007
qPCR	OS	3	277	2.11 (1.42–3.13)	< 0.001	17.7	0.297
Sample size
< 70	OS	9	535	2.25 (1.31–3.88)	0.003	75.5	< 0.001
	TTP	4	255	2.49 (1.51–4.10)	< 0.001	0.0	0.72
70–120	OS	10	903	2.37 (1.42–3.95)	0.001	55.9	0.02
	TTP	6	578	2.43 (1.09–5.44)	0.03	72.8	0.003
> 140	OS	9	2019	1.60 (1.18–2.18)	0.003	75.8	< 0.001
	TTP	4	882	1.98 (1.12–3.51)	0.019	63.2	0.043
Study type
Retrospective	OS	21	2807	1.82 (1.39–2.40)	< 0.001	81.5	< 0.001
	TTP	11	1273	2.32 (1.50–3.60)	< 0.001	57.9	0.008
Prospective	OS	7	650	1.98 (1.57–2.49)	< 0.001	0	0.6
	TTP	3	542	2.09 (1.03–4.23)	0.04	56.2	0.102
Cancer type
Digestive system tumor	OS	10	1528	1.79 (1.38–2.31)	< 0.001	40.8	0.085
Reproductive system tumor	OS	6	756	2.39 (1.53–3.72)	< 0.001	34.9	0.175
Bladder cancer	OS	2	182	2.90 (1.32–6.15)	0.006	0.0	0.521
Colorectal cancer	OS	2	238	2.32 (1.22–4.42)	0.01	0.0	0.655
Endometrial cancer	OS	2	145	6.64 (1.41–31.27)	0.017	0.0	0.99
Esophageal cancer	OS	2	501	1.76 (1.28–2.43)	0.001	0.0	0.79
Esophageal cancer	TTP	2	340	2.23 (0.91–5.49)	0.081	77.9	0.033
Gastric Cancer	OS	2	417	1.68 (1.22–2.32)	0.001	1.5	0.314
Melanoma	OS	2	164	1.95 (0.45–8.49)	0.376	84.8	0.01
Vulvar squamous cell carcinoma	OS	2	137	2.92 (1.69–5.04)	< 0.001	0.0	0.69
Age (Mean/Median)
< 60 years	OS	9	991	2.02 (1.22–3.36)	0.007	83.6	< 0.001
> 60 years	OS	10	1262	1.76 (1.16–2.67)	0.008	68.8	0.001
Follow-up (Median/Mean)
≤ 45 months	OS	8	1092	1.90 (1.29–2.78)	0.001	79.4	< 0.001
> 45 months	OS	8	783	3.41 (2.41–4.83)	< 0.001	0.0	0.97
Study quality
NOS score > 7	OS	18	2825	2.00 (1.48–2.69)	< 0.001	72.6	< 0.001
NOS score ≤ 7	OS	10	632	1.75 (1.20–1.57)	< 0.001	72.4	< 0.001

Abbreviations: HR hazard ratio, CI confidence interval, OS overall survival, TTP time to tumor progression, IHC Immunohistochemistry, qPCR Quantitative Real Time Polymerase Chain Reaction