Small extrachromosomal circular DNAs as biomarkers for potential pan-cancer diagnosis and prognosis
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Small extra chromosomal circular DNA (eccDNA) is a circular DNA molecule that is independent of conventional chromosomes and exists widely in eukaryotes[1]. Recently, small eccDNAs have been reported to be related to microRNA expression and innate immunostimulatory activities[2,3]. However, the formation mechanism and function of small eccDNAs, especially their role in carcinogenesis, need to be further explored. As small circular DNA molecules, small eccDNAs are promising biomarkers in cancer detection because they are structurally more stable than RNA and linear DNA[4,5]. However, it is still unclear whether the small eccDNA profile in cancer plasma can represent that in cancer tissues. Previous studies on small eccDNAs were mostly based on the short-read sequencer[6,7]. Small eccDNAs must be fragmented during sample preparation, thus losing the full-length information that is crucial for functional studies.