Table 1. The baseline characteristics of included studies.

Author, year	Ethnicity	Cancer type	Sample	Na	Male	Female	Survival	Analysis	mtDNA gene	nDNA gene	NOS score
Bai25	Asian	Breast cancer	Tissue	148	0	148	OS	MV	tRNA-Leu (UUR)	B2M	4
Chang26	Asian	Colorectal cancer	Tissue	194	134	60	DFS	MV	MT-CYB	RNase P gene	9
Chen20	Asian	Glioma	Blood	336	189	147	OS/PFS	MV	MT-ND1	HGB	7
Cui18	Asian	Colorectal cancer	Tissue	60	30	30	OS	UV	MT-ND1	β-actin	9
Dang27	Asian	Laryngeal cancer	Tissue	204	197	7	OS	MV	MT-ND2	β-actin	9
Feng, 2015	Asian	Cervical cancer	Tissue	122b	NA	NA	OS	MV	NC_012920 region	B2M	8
He21	Asian	HCC	Blood	618	544	74	OS/DFS	MV	MT-ND1	HGB	9
Lee22	Asian	Gastric cancer	Tissue	109	82	27	OS/DFS	UV	MT-COX1	β-actin	6
Lin28	Asian	Head and neck cancer	Blood	75	75	0	OS	UV	MT-tRNAleu	18 S	6
Mohideen17	Caucasian	Colorectal cancer	Blood	273c	160	116	OS/DFS	MV	MT-ND2	FASLG	8
Osch16	Caucasian	Colorectal cancer	Tissue	655c	372	306	OS	UV	D-loop	B2M	8
Qu29	Asian	Colorectal cancer	Blood	598	328	270	OS/DFS	MV/UV	MT-ND1	HGB	8
Tu, 2015	Caucasian	Prostate cancer	Blood	1266	1266	0	PFS	MV	MT-ND1	HGB	7
Wang30	Asian	Colorectal cancer	Tissue	124c	72	90	OS	UV	MT-ND1	β-actin	7
Weerts31	Caucasian	Breast cancer	Tissue	186b	NA	NA	DMFS	MV	MT-TL1	HMBS	7
Xu32	Asian	NSCLC	Tissue	128	95	33	OS	MV	NC_012920 region	B2M	8
Yamada33	Asian	HCC	Tissue	31	27	4	OS	UV	mtDNA	β-actin	8
Yu34	Asian	Breast cancer	Tissue	59	0	59	OS/DFS	UV	D-loop	β-actin	6
Zhang35	Asian	Gastric cancer	Tissue	103	84	19	OS	MV	MT-ND1	β-actin	8
Zhang36	Asian	Glioma	Tissue	124	68	56	OS	MV	MT-ND1	β-actin	8

^aNumber of included patients; ^bUnknown information of gender; ^cexisting missing data.

NOS: Newcastle-Ottawa Quality Assessment Scale; OS: overall survival; DFS: disease-free survival; PFS: progression-free survival; DMFS: distant metastasis-free survival; MV: multivariate analysis; UV: univariate analysis; NSCLC: non-small cell lung cancer; HCC: hepatocellular carcinoma.