Two people share the same exposures, the same risks, the same environment — and yet cancer unfolds differently in each of them, a mystery that has shadowed oncology for generations. An international research team studying over 580 liver tumors across genetically distinct mouse strains has now measured that unfairness with unusual precision, finding that identical carcinogens produce divergent tumor trajectories depending entirely on the host's genetic background. Though all tumors ultimately converged on the same MAPK signaling pathway, the routes they traveled — and the speed at which they ar