A cancer tumor’s ability to mutate allows it to escape from chemotherapy and other attempts to kill it. So, encouraging mutations would not be a logical path for cancer researchers. Yet a Mayo Clinic team and their collaborators took that counterintuitive approach and discovered that while it created resistance to chemotherapy, it also made tumors sensitive to immunotherapy. They also found that this approach worked successfully across tumor types and individual patient genomes. Their findings involving mouse models and human cells appear in Nature Communications.