Why do children develop cancer? An international team of researchers, led by Charité – Universitätsmedizin Berlin and the Memorial Sloan Kettering Cancer Center in New York, now reveal that mysterious rings of DNA known as extrachromosomal circular DNA can contribute to cancer development in children. Producing the first detailed map of circular DNA, the scientists have shed new unanticipated insights on long standing questions in the field of cancer genetics. The work has been published in Nature Genetics*.