It's a dog's lifeCanine transmissible venereal tumor is one of the few cancer lineages that is transferred among individuals through contact. It arose millennia ago and has been evolving independently from its hosts ever since. Baez-Ortegaet al.looked at the phylogenetic history of the cancer and describe several distinctive mutational patterns (see the Perspective by Maley and Shibata). Most notably, both positive and negative selection show only weak or distant signals. This suggests that the main driver of the lineage's evolution is neutral genetic drift. Understanding the influence of drift may reshape how we think about long-term cancer evolution.Science, this issue p.eaau9923; see also p.440