Identification and Characterization of Extrachromosomal Circular DNA in Plasma of Lung Adenocarcinoma Patients

BACKGROUND: Chromosome is the basic framework for eukaryotic cells to store genetic information, but certain genes exist in circulation, such as extrachromosomal circular DNA (eccDNA). The unique genetic characteristics and structure of eccDNA provide a new vision on the early diagnosis of cancer; however, whether eccDNA contributes to the early diagnosis and progression of lung cancer remains unclear. METHODS: We performed next-generation sequencing (NGS) analysis of eccDNA from the plasma of 6 lung adenocarcinoma (LUAD) patients. The data of plasma eccDNA of healthy people were obtained from public available database. We compared size distribution, chromosome origin, formation and expression patterns of eccDNA between LUAD patients and those of 6 healthy people and 4 healthy gravidas. RESULTS: A total number of 716,059 eccDNA ranging from 22 bp to 3,297,519 bp were detected with an average size less than 800bp and distinctive bimodality in size around 191 bp and 320 bp. After comparison of eccDNA abundance in each sequencing sample, nine eccDNA were ranked on top with higher frequency in lung adenocarcinoma patients than healthy people. Among them, four eccDNA (DOCK1, PPIC, TBC1D16, and RP11-370A5.1) were uniquely expressed in lung adenocarcinoma patients, which may serve as potential biomarkers for early diagnosis LUAD. CONCLUSION: Cancer-specific eccDNA was presented in LUAD compared to normal people, which might serve as a promising biomarker in LUAD.