NCIt definition : An extrachromosomal circular DNA located in the nucleus that is relatively small in
size and contains chromatin but lacks a centromere and telomeres. These circular DNAs
are found in tumor cells and are able to replicate during cell division during chromosome
replication. They often contain extra copies of oncogenes and/or genes involved in
drug resistance and lack transcription regulatory elements. Unregulated expression
of genes present in these structures may play a role in tumor growth and tumor cell
survival.;