Researchers at the University of Cambridge exposed genetically different mice to the same DNA damage and found that inherited genetic background influenced not only whether tumors developed but the evolutionary path those tumors took afterward. What this work adds is evidence that inherited background also shapes which mutations a tumor accumulates and which evolutionary route it follows once it has started. If that holds in humans, the implication would be that two people with the same inherited risk factor and the same exposure might still develop biologically different cancers requiring different treatment. The confirmed finding is that in a controlled mouse experiment, inherited genetic background shaped how tumors evolved after identical DNA damage. That in mice given the same DNA damage, inherited genetic background influenced both whether tumors developed and how those tumors evolved.