The scientists also identified 12 patterns of mutations present as tumours form and grow. Dr Emma Smith, Cancer Research UK's science information manager, said that the study brings scientists 'closer to getting a complete picture of the genetic changes at the heart of breast cancer and throws up intriguing clues about the key biological processes that go wrong in cells and drive the disease'.
Researchers took samples of breast cancers and their surrounding tissues from 560 people, including four male participants. The genomes of the cancer cells were sequenced and compared with the sequences of healthy cells, resulting in the identification of 93 mutations in the cancer cells.
While the majority of these mutations had already been shown to play a role in cancer development, five had not been formally flagged as risk genes. These include xbp1, a gene which regulates the expression of immune system genes, and foxp1, which codes for a protein involved in the activation of gene transcription.
By sequencing both sets of genomes, scientists were able to map the genetic mutations that present in each person's cancer, allowing them to observe that each cancer's genome is unique.
The researchers also picked out genetic patterns known as 'mutational signatures' that can be found in cancer cells. These signatures can be left behind by the types of damage which can lead to cancer, for example during some viral infections. Scientists hope that unpicking these signatures will lead to better understanding of how cancers grow and thus provide a route to better-targeted treatments.
Dr Serena Nik-Zainal at the Wellcome Trust Sanger Institute, who led the study, said: 'In the future, we'd like to be able to profile individual cancer genomes so that we can identify the treatment most likely to be successful for a woman or man diagnosed with breast cancer.'