Aneuploidy — the presence of an abnormal number of chromosomes — is a common feature of cancer cells, but it is unclear how specific patterns of aneuploidy arise. These authors developed a computational method for identifying candidate tumour suppressors and oncogenes on the basis of mutation patterns in tumour samples. They found evidence that there are many cancer-driving genes for which a continuum of oncogenic potential exists, and they propose that the specific combinations of these genes on chromosomes explain the patterns of aneuploidy that arise in cancer.