The chromosomal theory of inheritance dictates that genes on the same chromosome segregate together while genes on different chromosomes assort independently¹. Extrachromosomal DNAs (ecDNAs) are common in cancer and drive oncogene amplification, dysregulated gene expression and intratumoural heterogeneity through random segregation during cell division^(2,3). Distinct ecDNA sequences, termed ecDNA species, can co-exist to facilitate intermolecular cooperation in cancer cells⁴. How multiple …