Table 1. Characteristics of studies on the overall relationship between cigarette smoking and p16 methylation in lung cancer patients.

First author	Year	Location	Histology	Age(y)	Sample size(n)	p16 methylation in smoker	p16 methylation in nonsmoker
Sanchez-Cespedes [19]	2001	USA	NSCLC	66±3	47	7/33	5/14
Zochbauer-Muller [20]	2001	Australia	NSCLC	28–81	107	27/98	0/9
Kim [21]	2001	USA	NSCLC	67±11	185	49/172	2/13
Yanagawa [22]	2002	Japan	NSCLC	67±2	51	13/37	1/14
Toyooka [12]	2003	Asia-Pacific	AC	26–87	295	47/183	6/112
Toyooka [12]	2003	Asia-Pacific	SCC	26–87	189	58/172	5/17
Yanagawa [23]	2003	Japan	NSCLC	39–86	75	21/55	2/20
Toyooka [24]	2004	Japan	AC	No data	217	29/120	10/97
Toyooka [24]	2004	Japan	SCC	No data	138	46/130	1/8
Kim [25]	2004	Korea	SCC	No data	125	37/117	3/8
Divine [26]	2005	USA	AC	33–86	203	81/157	18/46
Liu [27]	2006	USA	NSCLC	65±10	122	51/81	13/41
Nakata [28]	2006	Japan	NSCLC	40–85	202	38/139	9/63
Toyooka [29]	2006	Japan	AC	No data	164	24/86	7/78
Georgiou [30]	2007	Greece	NSCLC	45–75	27	20/24	2/3
Guzman [31]	2007	Chile	NSCLC	66±9	65	39/54	10/11
Kim [32]	2007	Korea	NSCLC	41–82	99	18/79	4/20
Tessema [33]	2009	USA	AC	66	175	67/100	48/75
Wang [34]	2010	China	AC	46–84	56	9/20	10/36
Yanagawa [35]	2011	Japan	AC	39–86	62	7/36	2/26
Zhang [36]	2011	China	NSCLC	32–79	198	82/144	18/54