Table 1. Characteristics of studies included in the study.

				Case		Control			Control source	Control sample
Author	Year	Region	Age (case, years)	M	U	M	U	Method
Onerci Celebi[16]	2016	Turkey	mean = 56.6; range: 40–75	64	18	3	8	Pyrosequencing	H	tissue
Yang[17]	2015	China		27	50	12	50	MSP	A	tissue
Asokan[18]	2014	India		4	6	0	5	MSP	H	tissue
Bhatia[19]	2014	India	mean = 53.0; sd: 12.97	58	18	34	36	MSP	H	tissue
Rettori[20]	2013	Brazil		14	53	2	55	QMSP	H	saliva
Koutsimpelas[21]	2012	Germany	mean = 62.0; range: 45–83	13	10	0	3	MSP	H	tissue
Paluszczak[22]	2011	Poland	mean = 58.3; range: 41–75	22	19	15	26	MSP	A	tissue
Weiss[23]	2011	Germany	mean = 63.7; sd: 11.8	13	39	3	28	MSP	H	tissue
Su[24]	2010	Taiwan	mean = 54.94; range:37–82	7	23	3	27	QMSP	A	tissue
						0	12		H	buccal cell
Kordi[25]	2010	Iran	mean = 54.14	56	20	31	26	MSP	H	tissue
Steinmann[26]	2009	Germany	mean = 57.0; range: 41–77	29	25	7	16	MSP	A	tissue
De Schutter[27]	2009	Belgium		17	23	0	5	MSP	H	tissue
Righini[28]	2007	France	median = 57.0; range: 33–7	20	70	0	30	MSP	A	tissue
						0	30		H	saliva
						13	47		A	saliva
Martone[29]	2007	Italy	mean = 60.9; range: 27–89	10	10	5	6	MSP	A	tissue
Kato[30]	2006	Japan		27	24	0	18	MSP	H	tissue
						9	13		A	tissue
Maruya[31]	2004	USA	mean = 58.3; range: 31–81	10	22	7	25	MSP	A	tissue
						1	5	MSP	H	tissue
Kulkarni[32]	2004	India	mean = 50.0; range:25–71	31	29	16	44	MSP	A	tissue
						0	20	MSP	H	buccal cell
Viswanathan[33]	2003	India		21	30	0	25	MSP	A	tissue
Rosas[34]	2001	USA		7	23	4	3	MSP	A	saliva
						1	29		H	saliva
Sanchez[35]	2000	USA		31	64	14	15	MSP	A	serum

M: MGMT promoter methylated, U: MGMT promoter unmethylated

A: Autologous, H: Heterogeneous

sd: standard deviation