For generations, medicine has wrestled with a quiet mystery: why does the same carcinogen spare one person and claim another? An international team of researchers, working across Cambridge, Edinburgh, and institutions throughout Europe and America, has now produced the first direct evidence that inherited genetics fundamentally govern not only who develops cancer, but how tumors chart their course once they begin. By exposing genetically distinct mouse populations to identical conditions, they demonstrated that our DNA does not merely set a threshold for vulnerability — it actively shapes the