The simultaneous discovery of four genes linked to breast cancer was described as the biggest advance in the field for more than a decade.

The findings offer researchers new clues to identify which women are genetically predisposed to develop breast cancer and increases understanding of the disease.

Some low and medium risk genes have been identified since the 1990s but never before have researchers been able to identify them en masse. The latest genes identified were TNRC9, MAP3K1, LSP1 and FGFR2, while the genome region where a fifth is located is called 8q.

Professor Douglas Eaton, one of the lead researchers, said that while up to 10 per cent of breast cancer cases in Britain each year are caused by inherited genetic mutations, only a quarter of the genes responsible have been identified.

Each year in Britain there are 44,000 new cases of breast cancer and 12,500 die from it. In the early 1970s only half of breast cancer patients survived for five years but by 2002 the survival rate had been increased to 80 per cent through new treatments and improved diagnosis. Finding four more linked genes, and being close to a fifth, increases the proportion identified by 4 per cent but, moreover, it shows scientists how to find others.

“Now we know these search methods are effective, we think that many more breast cancer genes can be found,” said Professor Eaton, director of Cancer Research UK’s genetic epidemiology unit in Cam-bridge.

Women who have two faulty copies of the FGFR2 gene have a 40 to 60 per cent higher chance of developing breast cancer than those who have two normal copies. About one in six women carry the two faulty copies and would have a lifetime risk of breast cancer of about one in six, compared with one in eleven for those with two healthy copies.

Other mutations identified in the study raise the risk by smaller amounts, and are carried by between one in eleven and one in sixteen women.

The absolute risk, however, is significantly lower than that for mutations in the BRCA1 and BRCA2 genes. Over their lives, 80 per cent of women with such mutations will contract breast cancer.

As the new genes confer a much lower risk, it would not be worthwhile to screen women for them using current technology: most women with FGFR2 mutations, for example, will not get breast cancer. In the future, however, it could be possible to test for combinations of the genes that do raise the risk more significantly.

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