They have found that all families with an inherited risk of both cancers have the same gene defect, and they expect to locate the gene responsible within months.
Women who are found to be carriers - with a 60 to 80 per cent chance of developing the disease - can then be monitored with regular mammograms and ultrasound scans of their ovaries. Treatment with the drug tamoxifen may reduce the breast-cancer risk further, and prophylactic or preventive surgery would be an option. The at-risk women could decide to have healthy breasts and healthy ovaries removed in their thirties or forties.
The findings, published yesterday in the American Journal of Human Genetics, also provide clues to non-familial breast and ovarian cancer. Professor Bruce Ponder, of the human cancer genetics group of the Cancer Research Campaign and chairman of the committee that co-ordinated the international study, said: 'This is another piece in the jigsaw which will help us understand the biology of two cancers that currently affect tens of thousands of women in this country and claim the lives of 20,000 every year.'
The number of women from families with an inherited risk of breast and ovarian cancer is small, accounting for about 4 per cent of cases seen in breast-cancer clinics. But their additional risk of developing cancer compared with that of a woman who does not have the gene is high; by the age of 50 the risk is about 60 per cent, increasing to 80 per cent by the age of 80.
A total of 214 families took part in the study: 60 from the United Kingdom and others from the United States, the Netherlands, Germany, France, Iceland and Sweden. Some had a history of both breast and ovarian cancer, some of breast cancer alone. Dr Doug Easton, who leads the CRC team, said that all the families with the breast and ovarian cancer shared the same genetic defect. 'We believe that in tumours this particular gene, which is located on chromosome 17, is faulty so that it cannot function normally and a cancer develops.'
Many of the women in the study were recruited through press advertisements. Professor Ponder said that many more people were probably unaware that an excess of deaths from breast and ovarian cancers in their families were linked to an inherited predisposition to the diseases. He urged GPs to consider the possibility, and advised women who suspected they were members of an affected family to seek advice.
On the question of pre-emptive mastectomy, which is common in the US but rare in Britain and unpopular with many surgeons, Professor Ponder said that women known to carry the defect should be referred to a clinical geneticist to discuss the options. 'It is a very personal decision and depends on the individual. The decision is not much to do with the risks, more to do with how she can cope.'
The study is the result of collaboration between the CRC, the Institute of Cancer Research and the Imperial Cancer Research Fund genetics laboratory.Reuse content