Table 4. summary of the association between clinicopathological characteristics.

Characteristic	Number of studies	Number of patients	Pooled OR [95% CI]	P value	Model	Heterogeneity
						I2 (%)	P value
Tumor size
Alimentary system	5	639	1.84 [1.32, 2.58]	<0.001	Fixed	33	0.17
Reproductive system	1	123	2.78 [1.18, 6.57]	0.020	–	–	–
Nervous system	1	150	2.95 [1.51, 5.78]	0.002	–	–	–
Merged result	7	912	2.09 [1.58, 2.77]	<0.001	Fixed	28	0.19
Lymphatic invasion
Alimentary system	5	641	2.54 [1.68, 3.84]	<0.001	Fixed	0	0.64
Reproductive system	1	128	5.53 [0.70, 43.81]	0.110	–	–	–
Merged result	6	769	2.67 [1.78, 4.00]	<0.001	Fixed	0	0.59
Distant metastasis
Alimentary system	3	295	1.25 [0.32, 4.90]	0.08	Random	61	0.08
TNM grade
Alimentary system	4	559	2.23 [1.55, 3.21]	<0.001	Fixed	0	0.82
Histopathological grade
Alimentary system	5	550	2.35 [1.00, 5.51]	0.001	Random	75	0.001
Reproductive system	1	150	27.73 [9.18, 83.78]	0.003	–	–	–
Nervous system	1	111	4.22 [1.62, 10.98]	<0.001	–	–	–
Merged result	7	811	3.46 [1.46, 8.23]	0.005	Random	82	<0.001

OR, odds ratio; TNM, tumor node metastasis classification.