Table 1.

Characteristics of studies included in this meta-analysis

First author	Year	Location	Study design	p16 (M/U)b		pTNMa (M/U)b		Grade (M/U)b
				case	control	≤T1	≥T2	Low grade	High grade
Seyed Ali Hosseini	2010	India	Case-control	12/68	0/80	4/59	8/9	-	-
Sonata Jarmalaite	2008	Finland	Case-control	36/22	0/5	3/35	5/15	0/10	8/44
Hui-Hui Lin	2010	Taiwan	Case-control	20/37	0/20	19/13	13/8	9/10	23/15
M.T. Valenzuela	2002	Spain	Case-control	19/67	1/48	14/43	4/17	7/17	11/49
Michael W.Y. Chan	2002	Hong Kong	Case-control	26/72	0/11	-	-	2/7	1/12
Zbigniew Jabłonowski	2010	Poland	Case-control	17/25	0/36	-	-	-	-
Tohru Nakagawa	2005	Japan	Case-control	16/64	0/9	14/57	4/21	-	-
Yasuhiro Tada	2002	Japan	Case-control	6/49	0/5	-	-	1/4	5/45
Michael B. Scher	2012	Israel	Case-control	3/39	1/21	3/28	0/9	0/12	1/17
Stefan Hauser	2013	Germany	Case-control	33/62	9/44	-	-	-	-

pTNM (p, pathologic stage; T, tumor size; N, node status; M, metastatic status). Tumor grade ≤1 was defined as low-grade, and tumor grade ≥2 was defined as high-grade.

^aP, pathologic stage; T, tumor size; N, node status; M, metastatic status;

^bp16 methylated/p16 unmethylated.