Researchers at Queens University in Belfast have identified a gene that lies at the heart of some forms of breast cancer.
Their work centres on an early warning system gene that helps an immune system "radar" spot threatening cells.
They have found that in healthy women the BRCA-1 gene helps the body to detect potentially cancerous cells, which are then forced to self-destruct. But when the gene becomes faulty, the "radar" is blinded and tumours are allowed to develop.
They conclude that women with a defective BRCA-1 gene have a 65 per cent to 85 per cent chance of developing breast cancer at some point in the their lives. They also have an increased risk of ovarian cancer.
Scientists already knew that BRCA-1 was important in repairing gene damage that can lead to cancer. But the new work by Dr Paul Harkin's team suggests the gene is also involved in spotting damaged cells.
Professor Patrick Johnston, director of the University's Cancer Research Centre, said: "These results are beginning to shed light on why some women have such a high risk of developing breast cancer.
"Now we can see that the faulty gene also impairs the body's ability to spot cells that are becoming cancerous. This combination of problems may explain the gene's devastating effects".
PA