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Scientists' understanding of how cancers develop is being rewritten by a new discovery in cell biology. The mechanisms that control cells dying may be the most crucial aspect of regulating the body, not simply unavoidable waste as had been thought.

The conventional view has been that a tumour grows because cells start proliferating out of control. But scientists have now discovered that the cells in tumours probably grow at the same rate as ordinary tissue. It is the messages that tell them to die that are not getting through.

The findings open up new avenues in the search for drugs to combat cancer, as scientists hunt for a new set of genes that control cell death, rather than studying cell production and proliferation.

Gerard Evan of Imperial Cancer Research Fund, who spoke at the "Genetics of Death" conference held by the Genetical Society in Glasgow last week, said that all cells die unless they receive constant signals that tell them to stay alive. "It's totally counterintuitive," he said. "But cells in your body are cheap, so the body bins them if they have anything wrong with them. Cancer can only arise if something suppresses cell death. It's not just about them proliferating uncontrollably - it's about them surviving uncontrollably. It means that there's a whole repertoire of mutations out there about which we know very little and which are the keys to cancer."

Now scientists are hunting for the "engine of cell destruction", he said. A set of novel enzymes, proteolytic enzymes, has just been discovered by Junying Yuan of Boston University. They cause the cell to self-destruct. The enzymes have not been discovered before because scientists were not looking for them.