Table 1 Classification of eccDNA

spcDNA

100–10 kb

Homologous to repetitive chromosomal sequences; byproducts or intermediates of gene rearrangement

Initiation and enhancement of genomic instability

telomeric circles

Integral multiples of 738 bp

Duplex or single-stranded molecule composed of telomeric repeats

Involved in the ALT of telomeres

microDNA

100–400 bp

Origin from regions with high GC content and exon density

Expressing functional small regulatory RNAs, including microRNAs and new si-like RNAs

ecDNA

1–3 Mb

Acentric, without telomere, containing full genes

Amplifying genes related to carcinogenesis and drug resistance