Cancer experts have identified a gene which can cause a particularly aggressive form of breast cancer to develop.
ZNF703 is the first "oncogene" to be discovered in five years.
It is overactive in around one in 12 breast cancers, and could account for up to 4,000 UK cases a year.
Cancer Research UK, whose scientists carried out the work, said the gene was a "prime candidate" for the development of new breast cancer drugs.
An oncogene is one which would normally help instruct healthy cells to divide but if it becomes overactive, it upsets the normal checks and balances that control that process.
That damage is described as being "like a car's accelerator becoming stuck down", and the cell and all its daughter cells are permanently instructed to divide.
Her2 - another oncogene - is already tested for. The drug Herceptin was developed to treat Her2 positive breast cancers. BBC News
