New rapid methods of decoding DNA have brought to light a catastrophe that can strike human cells: a whole chromosome may suddenly shatter into pieces. If the cell survives this disaster, something worse may ensue: the cell becomes cancerous. The finding marks a striking exception to the current theory of how cancer develops. Cells are thought to become cancerous over many years as they collect, one by one, the mutations required to override the many genetic restraints on a cell's growth. It now seems that a cell can gain all or most of these cancerous mutations in a single event.