Horvitz Lab researchers discovered a trigger for cell extrusion—a mechanism for eliminating unneeded cells—and suggest that the process might provide a natural defense against cancer. In a study appearing in Nature, researchers found that in the worm C. elegans many of the genes necessary for extrusion are involved in the cell division cycle. However, as extruded cells enter the cell division cycle, they are unable to replicate their DNA and consequently experience replication stress. Collaborators’ studies of mammalian cells revealed that replication stress similarly drives the extrusion of mammalian cells and that the well-known tumor suppressor protein p53 plays a role in the extrusion of cells undergoing DNA replication stress. Because cancerous and precancerous cells commonly experience replication stress, the findings indicate that extrusion may be a tumor suppression mechanism.