Nature Cell Biology, Published online: 06 August 2026; doi:10.1038/s41556-026-02032-5 In clonal haematopoiesis, pre-cancerous mutant blood cells induce premature senescence in bone marrow stromal cells, creating an environment that allows mutant blood cells to outcompete healthy ones. Clearing senescent stromal cells reduces mutant clone expansion and delays progression to blood cancer in mouse models, which highlights a potential strategy for cancer prevention.