Free circulating mitochondrial DNA in blood of melanoma patients

1904 Genetic changes in mitochondrial DNA (mtDNA) cause a variety of diseases including cancers. The mtDNA is particularly susceptible to mutations because of a high level of reactive oxygen species generation that produce mtDNA mutations in mitochondria and a low level of DNA repair system. Somatic mtDNA mutations are identified in various human carcinomas, and most mutations are found in the displacement loop (D-loop) region of mtDNA. We hypothesized that malignant melanoma frequently has genetic alterations in the D-loop region and mtDNA alterations detected in the blood are available as a circulating DNA melanoma marker. D-loop region from 20 melanoma cell lines, 12 melanoma specimens and corresponding lymphocytes and plasma samples were sequenced using CEQ 8000 XL Genetic Analysis System (Beckman Coulter). Subsequently, the D-loop region in paired lymphocytes and plasma obtained from 32 melanoma patients was sequenced. Nine of 20 (45%) melanoma cell lines and 5 of 12 (42%) melanoma specimens contained somatic mutations in the D-loop region of mtDNA. DNA alterations in the poly-cytosine tract (C-tract) of D-loop were detected in 6 of 20 (30%) cell lines and 2 of 12 (17%) specimens. Two of 5 paired plasma samples (40%) contained the same mutations as melanoma specimens. In comparison between lymphocytes and plasma, 9 of 44 paired plasma samples (20%) contained at least one mutation compared to corresponding lymphocytes. Somatic mutations in the D-loop region of tumor and paired plasma did not correlate with clinicopathological characteristics. However, circulating mtDNA alterations were more frequent in advanced disease (AJCC stage I, 0%; stage II, 0%; stage III, 18%; stage IV, 25%). Studies suggest that circulating mtDNA mutations in plasma in melanoma patients can be detected.