A method for parallel sequencing of single-cell extrachromosomal circular DNA (ecDNA) and full-length mRNA transcriptomes has enabled new insights into the roles of ecDNA in cancer progression, researchers from Charité hospital and the Max Delbrück Center for Molecular Medicine reported in Nature Genetics on May 8, 2023. Circular DNAs are present in at least a third of cancer cells, and their presence correlates with poor prognosis in many cases. They can carry driver genes that have separated themselves from their chromosome of origin, and some research suggests that they serve as “reserve copies” of driver genes. Boundless Bio Inc. is in phase I trials targeting ecDNAs.