Table 1. Characteristics of the studies included in the meta-analysis.

Study	Year	Country	Ethnic	Method	Source of control	Cancer type	Case/control	SNP.	NOS
Tan[14]	2015	China	Asian	iMLDR	Population	HCC	395/686	1,2,3	7
Sun[20]	2015	China	Asian	PCR-RFLP	Hospital	CRC	257/236	1,2,3	7
Yin[22]	2015	China	Asian	SNPscan	Hospital	GAC	234/476	2,3	7
Jafarzadeh[35]	2015	Iran	Asian	PCR-RFLP	Population	BC	100/100	3	6
Winchester[36]	2015	USA	Caucasian	MassArray	Population	PC	566/530	3	9
Saxena[15]	2014	India	Asian	PCR-RFLP	Population	HCC	59/153	3	6
wang[37]	2013	China	Asian	PCR-RFLP	Population	OSC	106/210	1,2,3	7
Sun[38]	2013	China	Asian	SNPscan	Hospital	EC	380/380	3	8
Jaiswal[39]	2013	Indian	Asian	PCR-RFLP	Hospital	BLC	200/200	3	6
Tao[40]	2012	Mixed	Asian	PCR-RFLP	Population	EC	426/432	1,3	6
Sima[41]	2012	China	Asian	PCR-RFLP	Hospital	BT	170/222	2,3	7
Kaarvatn[42]	2012	Croatia	Caucasian	TaqMan	Mixed	BC	191/194	3	6
Carvalho[26]	2012	Brazil	Mixed	PCR-RFLP	Population	CC	162/76	3	6
Roszak[25]	2012	Poland	Caucasian	PCR-RFLP	Population	CC	405/405	1,3	7
Hu[43]	2012	China	Asian	PCR-RFLP	Hospital	OC	92/38	3	6
Huang[21]	2012	China	Asian	PCR-RFLP	Hospital	CRC	410/450	3	6
Liu[16]	2011	China	Asian	PCR-RFLP	population	HCC	869/891	1,2,3	9
Chaaben[44]	2011	Tunisia	African	Taqman	population	NPC	247/284	3	6
Ter-Minassian[45]	2011	USA	Caucasian	MassArray	Population	BT	261/319	2	8
Yang[19]	2011	China	Asian	Taqman	Hospital	HCC	608/612	3	6
Wu[24]	2009	China	Asian	PCR-RFLP	Population	GC	1035/1073	3	7
Chen[46]	2009	China	Asian	PCR-RFLP	population	CC	404/404	1,2,3	9
Miteva[13]	2009	Bulgaria	Caucasian	PCR–RFLP	Hospital	CRC	85/134	3	6
Wei[47]	2009	China	Asian	PCR–RFLP	Hospital	NPC	302/310	3	6
Zhao[48]	2009	China	Asian	PCR–RFLP	Hospital	BT	210/220	3	6
Ognjanovic[17]	2009	USA	Caucasian	Taqman	population	HCC	117/223	3	9
Han[27]	2008	Korea	Asian	PCR–RFLP	Hospital	CC	150/179	3	7
Hou[23]	2007	USA	Caucasian	TaqMan	Population	GC	257/428	1	6
Lee[49]	2007	USA	Asian	TaqMan	Population	LC	119/113	1	8
Wang[50]	2006	USA	Caucasian	TaqMan	Population	NHL	1130/941	1,3	9
Nieters[18]	2005	China	Asian	PCR–RFLP	Hospital	HCC	250/250	3	8
Howell[51]	2003	UK	Caucasian	ARMS-PCR	Hospital	CMM	145/229	3	7

PCR: polymerase chain reaction; RFLP: restriction fragment length polymorphism; HCC: hepatocellular carcinoma; GC: gastric cancer; CRC: colorectal cancer; BC: breast cancer; PC: prostate cancer; OSC: osteosarcoma; EC: esophageal cancer; BLC: bladder cancer; BT: brain tumor; CC: cervical cancer; OC: ovarian carcinoma; NPC: nasopharyngeal cancer; GC: gastric cancer; LC: lung cancer; NHL: non-Hodgkin lymphoma; CMM: cutaneous malignant melanoma. SNP No.1: rs568408 (3′ UTR G>A) in IL-12A; 2: rs2243115 (5′UTR T>G) in IL-12A; 3: rs3212227 (3′ UTR A>C) in IL-12B; NOS: the Newcastle-Ottawa Scale.