Genetic test will identify those most at risk of breast cancer
Published 26/06/2008 | 09:08
The chances of getting breast cancer vary more than sixfold among women because of their genetic inheritance but the breast screening programme fails to target those at highest risk, scientists have found.
Researchers at the University of Cambridge say it may soon be possible to offer women a genetic test based on the seven common gene sites that determine cancer risk and to focus prevention efforts accordingly.
Currently doctors only test women with a very strong family history of breast cancer for the high-risk genes such as BRCA1 and BRCA2. These gene faults increase the chances of a woman developing cancer from around 9 per cent to 80 per cent. But they are rare and few women benefit from such testing.
There are other common genetic variations that modestly increase the risk – but when they occur together they have a substantial effect. Around 3,300 women in the UK carry the low risk genes for each of the seven gene sites identified, who have less than half the risk of breast cancer of the general population – a 4.2 per cent lifetime risk compared with a 9.4 per cent risk.
At the other end of the scale, around 400 women have high risk genes for each of the seven sites, giving them a 23 per cent risk of developing breast cancer – two and a half times that of the population as a whole.
The remainder of the female population is distributed between these extremes and the researchers say genetic testing could provide each woman with an assessment of her risk of breast cancer, which could be used to target the screening programme.
Currently all women over 50 are invited for breast screening every three years and they have a 2.3 per cent risk of developing breast cancer over 10 years, averaged over the whole population. With genetic testing it would be possible to offer breast screening to all women with at least the same risk (2.3 per cent) but regardless of age. A woman of 40 with a 3 per cent risk would be offered screening while a woman of 55 with a 1 per cent risk would not.
Paul Pharaoh from the University of Cambridge, who led the study, published in The New England Journal of Medicine, said: "It is about tuning the screening programme to make it more efficient. You would screen the same number of women but pick up more cancers by targeting it on those at highest risk.
"We are a few years away from a new and powerful range of genetic tests for breast cancer. Genetic testing has the potential to identify women [under 50] at increased risk who would benefit from mammography at an early age... and also to identify women [over 50] with a low risk of breast cancer who may not need such regular checks."
Dr Lesley Walker, director of cancer information at Cancer Research UK, which funded the research, said: "This study marks the potential for a tailor-made approach to screening for breast cancer which could radically change who we target and how we detect early signs of the disease. Great progress has been made in our understanding of the ways in which certain genes affect the risk of breast cancer. But there is still some way to go before this kind of genetic profiling becomes a reality."