Detection of mitochondrial DNA alterations in primary tumors and corresponding serum of colorectal cancer patients

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Abstract
We previously examined colorectal cancer patients using mutation‐specific mismatch ligation assay for genetic alterations in primary tumors and paired serum samples and proved that genetic alterations present in the tumors of cancer patients can be detected in the serum of those same patients. Recent evidence has proved that various cancers frequently have mutations in the D‐loop region of mitochondrial DNA (mtDNA). Therefore, we thought that mutations in the mitochondrial genome might also become a genetic marker of colorectal cancer to detect tumor DNA in the serum of patients. We first sequenced the D‐loop region of mtDNA in colorectal cancers. We then proceeded with a sensitive method, i.e., mismatch ligation assay to examine the possibility that mtDNA alterations can be found in the serum DNA. We analyzed the D‐loop region of mtDNA in 77 primary colorectal cancers, 7 of which (9%) contained true somatic mutations in this region. We then examined whether mtDNA alterations can be found in the serum DNA using mismatch ligation assay. Of 7 alterations that were examined, 1 (14%) could be detected in the serum. This result suggested that the mtDNA alteration could also be used as a tumor marker to detect tumor DNA in the serum.