Nine new genes have been found linked to breast cancer, British scientists revealed last night.
The genes bring the total linked to the disease up to 40.
The latest discovery follows the announcement last month that breast cancer should now be considered ten different diseases.
Researcher Professor Mike Stratton, director of the Wellcome Trust Sanger Institute, Cambridgeshire, UK, said the researchers had found 70 different combinations of cancer mutations that could cause breast cancer.
The findings, reported in Nature, come from a study of 21,000 genes from 100 women with breast cancer.
Professor Stratton said: "The picture is certainly more complicated than we would have wanted, but as with many other things knowledge is our strongest weapon.
"These comprehensive insights reveal the faulty wiring of the cellular circuit board that causes cells to behave as cancers.
"Understanding our enemy at this level of detail will allow us to take more rational approaches to therapy, to understand why some cancers respond to drugs and others do not, and direct us to new vulnerabilities to be exploited in new treatments."
Fellow researcher Professor Andy Futreal said: "One of the most striking things about breast cancer is how it progresses differently in each patient and how each patient responds differently to therapy.
"Our results can help us to understand these differences."
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