Table 1.

Association between the mtDNA copy number and the risk and prognosis in CRC.

Sample type	Findings	Potential utility	Association	Ref
Cancer, adenoma, and adjacent normal tissue from CRC patients (n = 56) and recurrent CRC (n = 16); colon mucosa samples from healthy subjects (n = 76).	MtDNA copy number in carcinoma tissues and adjacent tissues was lower than that in earlier resected adenoma tissues and MtDNA copy number in primary CRC tissues was lower than that in recurrent CRC tissues.	Prognosis evaluation	The association between mtDNA and survival seemed to follow an inverse U-shape with the highest HR observed in the second quintile of mtDNA copy number (HR = 1.70, 95% CI = 1.18, 2.44) compared to the first quintile.	[20]
Colorectal cancer tissues (n = 65) and the corresponding noncancerous tissues.	The mean relative mtDNA copy number in colorectal cancer tissues was higher than that in noncancerous tissues.	Risk evaluation	Increased in the CRC tissues.	[33]
Colorectal adenoma tissues (n = 412) and cancer-free controls (n = 526).	There was no association between logarithmically transformed relative mtDNA copy number and colorectal adenoma risk.	Risk evaluation	No association.	[25]
Colorectal cancer tissues (n = 274) and the corresponding noncancerous tissues.	The mtDNA copy number was increased in 60.4% of the CRC tissues. But there was no association between the mtDNA copy number and the prognosis.	Risk evaluation and prognosis evaluation	Increased in the CRC tissues but no association with the prognosis.	[23]
Colorectal cancer tissues (n = 9) and cancer-free controls (n = 9).	The mtDNA copy number was decreased in adenocarcinoma.	—	Decreased in adenocarcinoma.	[41]
Leukocyte CRC patients (n = 598).	Patients with high leukocyte mtDNA content showed worse overall survival (OS) and relapse-free survival (RFS).	Prognosis evaluation	Negative correlation between leukocyte mtDNA content and prognosis.	[27]
peripheral leukocytes from CRC (n = 444) and controls nested (n = 1,423).	Baseline mtDNA copy number was lower among women who subsequently developed colorectal cancer.	Risk evaluation	Lower in colorectal cancers.	[28]
Colorectal cancer tissues (n = 60) and the corresponding noncancerous tissues.	The mtDNA copy number was lower in CRC tissues and it was correlated with lymph-node metastasis. Patients with a lower mtDNA copy number tended to have lower 3-year survival.	Risk evaluation and prognosis evaluation	Decreased in the CRC tissues.	[42]
Colorectal cancer tissues (n = 44) and the corresponding noncancerous tissues.	The mtDNA copy number was increased in the CRC tissues and this increase was particularly noticeable in stages I and II.	Risk evaluation	Increased in the CRC tissues.	[43]
422 colorectal cancer cases (168 cases with prediagnostic blood and 254 cases with postdiagnostic blood) and 874 controls who were free of colorectal cancer among participants.	There was a U-shaped relationship between the relative mtDNA copy number and colorectal cancer risk. The lowest and highest quartiles of relative mtDNA copy numbers were 1.81 (1.13–2.89) and 3.40 (2.15–5.36), respectively.	Risk evaluation	U-shaped association between the relative mtDNA copy number and risk of colorectal cancer.	[26]
Colorectal cancer tissues (n = 54) and the corresponding noncancerous tissues.	The mtDNA copy number was increased in the CRC tissues.	Risk evaluation	Increased in the CRC tissues.	[44]
Colorectal cancer tissues (n = 25) and the corresponding noncancerous tissues.	The mtDNA copy number was decreased in CRCs.	Risk evaluation	Decreased in the CRC tissues.	[45]

The mitochondrial DNAs copy number was different between individuals and between the tissues in human cells. Changes of mtDNA copy number were widely reported in CRCs. The PCR was used as the most common method to detect the mtDNA copy number in the tissues. There were contradictory points of the association between the mtDNA copy number and the risk and prognosis in CRC.