Table 2. Subgroup meta-analysis of pooled HRs for OS.

Categories	Studies (n)	Total cases	Fixed-effects model		Heterogeneity
			HR (95% CI) for OS	P-value	I2 (%)	Ph
[1] OS	7	674	2.13 (1.71–2.65)	< 0.001	0	0.54
[2] Cancer type
1) Digestive system	3	326	1.88 (1.30–2.73)	< 0.001	0	0.77
2) Nervous system	2	115	2.21 (1.43–3.42)	< 0.001	0	0.32
3) Respiratory system	1	173	2.76 (1.85–4.12)	< 0.001	N/A	N/A
4) Reproductive system	1	60	1.40 (0.71–2.76)	0.33	N/A	N/A
[3] Cut-off (high/low)
Median	5	432	1.91 (1.41–2.58)	< 0.001	0	0.60
Others	2	242	2.41 (1.75–3.31)	< 0.001	16	0.28
[4] Sample sizes
> 100	3	445	2.25 (1.67–3.03)	< 0.001	17	0.30
≤ 100	4	229	2.00 (1.45–2.76)	< 0.001	0	0.50
[5] Duration of follow-up
≤ 40 months	2	167	1.89 (1.19–3.00)	0.007	0	0.47
> 40 months	5	507	2.21 (1.72–2.83)	< 0.001	4	0.39