An international team of researchers has identified five new genetic variations that affect a woman's risk of developing breast cancer. Four of the variants are linked to genes that could play a role in the disease process, say the scientists, who published their findings in the journal Nature. Lead author Professor Douglas Easton, of Cancer Research UK's Genetic Epidemiology Unit in Cambridge, says that similar studies are underway to identify genes involved in prostate, bowel and lung cancer.
Around 5-10 per cent of breast cancer cases are caused by mutations in genes such as BRCA1 and BRCA2. But in most patients, the disease is triggered by the combined effect of many different genetic variations and non-genetic factors such as diet. Uncovering the genes involved in the 'non-hereditary' form of breast cancer has proved to be a long and arduous process, as each individual gene variant makes only a small contribution to a person's overall risk.
The latest research was a 'genome-wide association' (GWA) study, an approach that has already proved successful in identifying genes that play a role in other common conditions such as diabetes and obesity. It involves comparing large numbers of DNA samples taken from patients and healthy individuals, and looking at thousands of 'SNPs' - a type of genetic variation that affects just a single 'letter' of the genetic code. In the breast cancer study, the researchers looked at DNA from nearly 50,000 women, and pinpointed five SNPs that appear to affect the risk of breast cancer.
Two of the genes identified, called FGFR2 and TNRC9, are thought to increase the chances of breast cancer by about 20 per cent in women who carry one copy of the 'risk' variant, and perhaps by between 40 per cent and 60 per cent in those who carry two copies. This means that the lifetime risk for women with two risk variants in either of these two genes would rise from one in 11 to around one in six or seven. The other two genes, called MAP3K1 and LSP1, increase risk by 10 per cent in women who inherit one copy of the variants.
UK cancer specialist Professor Karol Sikora told BBC News Online: 'It's likely many more cancer predisposing genes will be identified using similar approaches in the next few months', adding 'I suspect that in the next three years it will be possible to separate a group of women into those that have a very high chance of getting breast cancer, those that have a very low chance and those that are in the middle'. Lead author Professor Bruce Ponder stressed that researchers did not yet know how these genes interacted with each other, adding 'We'll continue to search for more genes, but we'll also focus on unravelling this information so that we're ready to offer advice to women who may carry one or more of these faulty genes in the future'.
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