Table 1.

Characteristics of the included studies

Authors	Years	Samples		Sex status		Smoking history		Pathological types		Clinical staging
		Cases	Controls	Male	Female	Yes	No	Squamous cell carcinomas	Adenocarcinomas	I	II	III and IV
Zochbauer-Muller et al24	2001	107	104	76	31	98	9	43	45	61	21	25
Yanagawa et al25	2003	75	75	54	21	20	55	29	43	24	33	42
Russo et al26	2005	49	49	–	–	22	5	–	–	–	–	–
Tsou et al27	2005	7	11	–	–	–	–	–	–	–	–	–
Kim et al28	2007	88	88	70	18	72	16	53	35	51	37
Tan et al29	2007	20	10	–	–	–	–	–	–	–	–	–
Feng et al30	2007	49	49	26	23	–	–	14	20	21	17	–
Wang et al31	2007	28	12	17	11	–	–	7	15	–	–	–
Wang et al32	2008	95	95	19	76	–	–	35	45	31	26	34
Vaissiere et al33	2009	209	164	171	38	173	36	121	58	–	–	–
Begum et al34	2011	76	30	40	36	–	–	26	36	41	17	11
Guzman et al35	2012	26	33	26	33	–	–	25	7	–	–	–
Zheng et al36	2012	37	37	26	11	–	–	15	17	–	–	–

Note: “–” means data not available.