Researchers at Cambridge University in the UK have discovered mutations in the DNA of four genes that could play a significant role in triggering breast cancer in women.
The discovery would help evolve new methods of targeting younger women at higher-than-average risk of breast cancer so that they could be screened with mammography before they reach 50 - the age when routine breast screening now begins.
Unlike other genetic variations associated with familial breast cancer, the mutations in these four new genes are relatively common in the population and appear to form part of a bigger community of genes that play a role in breast-cancer predisposition.
However, the wider significance of the genetic discovery is that it brings the day closer when anyone's genome - the entire DNA blueprint - can be screened for the many hundreds of genes that are believed to increase susceptibility to a wide range of cancers.
Some scientists believe that the latest studies, published online in the journals Nature and Nature Genetics, are among the most important in the field of breast cancer since the first susceptibility genes for inherited forms of the disease were identified in the mid-1990s.
"This set of incredible scientific studies points to the future understanding of the genetics of cancer," said Professor Karol Sikora, a leading cancer specialist, who was not directly involved with the latest work.
"In theory, it allows you to look at thousands of people to study their genes and to find associations that we just didn't see before," Professor Sikora said. Several teams of scientists took part in the latest studies, with the biggest led by Douglas Easton, a professor of cancer epidemiology at Cambridge University, who studied the DNA of nearly 50,000 women, half of whom had breast cancer.
The scientists used "DNA chips" to screen each person's genome for genetic variations that were found to be strongly linked with breast cancer. Small variations in four genes emerged as the most likely associations. "We're very excited by these results because the regions we identified don't contain previously known inherited cancer genes," Professor Easton said.
"This opens the door to new research directions. Only very recent advances in technology have allowed us to carry out such a large comparison study," he said. Already, the scientists are applying the same approach to other cancers, such as prostate, lung and bowel cancers, in the hope of identifying genetic changes that can trigger a higher risk of developing any of the diseases.
Breast cancer is one of the most common forms of cancer in British women with some 44,000 new cases diagnosed each year. Inherited forms of breast cancer that are known to run in families account for between 5 and 10 per cent of cases. These genes - called BRCA1 and BRCA2 - were the first to be identified in the mid-1990s. Two of the four new genes are relatively common. For instance, between one in six and one in 16 women are estimated to carry two faulty copies of one of these genes.
The three other genes identified in the study are also common among the population but carry a lower risk of disease, said Cancer Research UK, which helped to fund the study. Professor Bruce Ponder, one of the leaders of the study and director of Cancer Research UK's Cambridge research institute, said that the new technique has greatly accelerated the rate at which cancer genes can be found.
"We have been able to search two thirds of the genome in one go. Rather than fish for new genes one at time with a rod and line, we have trawled the pool," Professor Ponder said. "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," he said.
"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," he added.