Epithelial cells, which line the surfaces and organs of the body, can protect themselves against cancer by removing unhealthy or abnormal cells through a mechanism known as "apical extrusion," where the damaged cells are forcibly removed from the cell layer by the surrounding healthy cells. The underlying process by which the defenses of apical extrusion are overcome, allowing cells to become invasive and cancerous, has remained unknown. Now, however, a group from Osaka University have identified that a molecule called Src is key in this process.