Scientists have developed a new technique to identify genes that increase the chance of women developing breast cancer.
Hundreds of genes may be linked to breast cancer
They hope it will lead to a single blood test which would reveal a woman's risk of getting the disease.
Researchers say the new technique speeds up gene identification and could mean finding all the genes associated with breast cancer.
Cancer Research UK described the development as "hugely significant".
Scientists found two genes responsible for breast cancer two years ago.
But now new research led by Cancer Research UK's Cambridge Research Institute, published in the Nature journal, has found five more.
It used to take decades to go through a patient's DNA and find faulty genes, but the newly-developed technique now makes the process much faster.
It compares significant parts of the patient's DNA with a healthy volunteer's and the differences are judged most likely to be the genes responsible for the disease.
This computer-based process can be completed in just a few hours and scientists believe that, within a few months, researchers could find all the genes involved in the development of breast cancer.
To find the four new genes, they sifted through the DNA of nearly 50,000 women, half of them breast cancer patients and half healthy.
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."
He told BBC Five Live that if more genes were identified it may help prevent the disease because people who were at "particularly high risk of the disease" could be identified.
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.
Currently, doctors only test for four genes, BRCA1, BRCA2, TP53 and PTEN, as these are associated with high risks of developing cancer.
But 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."
Lead author Professor Bruce Ponder, Director of Cancer Research UK's Cambridge Research Institute at the University of Cambridge, said researchers did not yet know how these genes interacted with each other.
He added: "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."