Cancer Research UK scientists led an international team of experts in the world's first large-scale "whole genome search" for breast cancer genes says the Nature Journal.

The researchers studied the DNA of nearly 50,000 women, half of them breast cancer patients and half healthy.

It is hoped their discovery will lead to more genes being identified, and better methods of identifying women most at risk.

By studying the genetic material researchers found five culprit DNA regions housing four new genes, FGFR2, TNRC9, MAP3K1 and LSP1.

Professor Douglas Easton, director of Cancer Research UK's genetic epidemiology unit in Cambridge, said: "Now we know these search methods are effective, we think that many more breast cancer genes can be found. "These methods are already being applied by Cancer Research UK to find genes for a whole range of other cancers, including prostate, bowel and lung cancer."

Overall, inherited cases make up between 5 and 10% of all breast cancer cases in the UK which total 44,000 a year. "Lifestyle factors" such as smoking and environmental factors are believed to account for the rest.

The new genes identified are far more common in the population than the well-known BRCA1 and BRAC2, but carry a lower risk, between 50% and 85% of women with BRCA1 or BRCA2 will develop breast cancer in their lifetime. In comparison, about 14% of women with one of the new genes would develop breast cancer.

This relatively small increased risk makes genetic testing for the four new genes - FGFR2, TNRC9, MAP3K1 and LSP1 - unsuitable, say the researchers, but as more of these "low risk" genes are found, it may be possible to design tests for a combination of genes, they say.

Currently, doctors only test for four genes, BRCA1, BRCA2, TP53 and PTEN, as these are associated with high risks of developing cancer.

They believe there are hundreds more breast cancer genes to be found.

Leading cancer specialist Professor Karol Sikora said: "It's likely many more cancer predisposing genes will be identified using similar approaches in the next few months.

"By risk banding women we will be able to target screening programmes far more effectively as well as developing tailored prevention strategies just for those most likely to get cancer.

"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.

"So all our screening programmes will be targeted for the very high risk and therefore be much more efficient."

Lead author Professor Bruce Ponder, Director of Cancer Research UK's Cambridge Research Institute at the University of Cambridge, added: "At the moment we don't know how these genes interact with each other or with lifestyle factors, each of which might increase the risk.

"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."

The whole genome analysis technique used by the researchers enabled them to study all the significant pieces of DNA code they wanted in one go, taking just a few hours.

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