A "landmark" study that divides types of breast cancer into 10 new categories could change the way the disease is treated forever, scientists said today.
Researchers examined the genetic make-up of 2,000 tumours in what was the largest such study of breast cancer tissue in the world, the culmination of decades of work.
They found that instead of one disease, breast cancer can be seen as an 'umbrella' term for at least 10 separate diseases.
It is hoped the categorisation of breast cancer, teamed with the discovery of new breast cancer genes, could provide more targeted treatments for women in the future and allow doctors to better predict patients' chances of survival.
The discovery of new genes could also help scientists to find out how gene faults cause the cancer to develop and lead to the creation of new types of drugs.
The research was carried out by Cancer Research UK scientists and its results are published in science journal Nature today.
Dr Harpal Kumar, chief executive of Cancer Research UK, said: "This is a landmark study that really changes the way we think about breast cancer - no longer as one disease but actually as 10 quite distinct diseases, dependent on which genes are really switched on and which ones aren't for an individual woman.
"It's the culmination of decades of research but really with some quite remarkable results from this study.
"What this research will help us to do is make a much more accurate, much more precise, diagnosis for every patient with breast cancer in the future.
"That will enable us to make sure that we really target the right treatment to the right woman based on those who are going to benefit, or if they're not going to benefit, not exposing them to the side-effects associated with those treatments.
"That will enable us to make much more progress in breast cancer in coming years."
He added: "There is huge reason to be optimistic about what is going to happen."
Up until now, breast cancer had been classified into four subgroups, depending on whether sufferers are oestrogen receptor positive or negative, and either tested as positive or negative for the HER2 protein.
Professor Carlos Caldas, senior group leader at Cancer Research UK's Cambridge Research Institute, said: "The two main findings are that we have a completely new way of looking at breast cancer, no longer as three or four diseases but at least 10 subtypes that we very robustly can identify using this method.
"The other thing is that because we are looking at these tumours at a great level of detail, we can discover new genes."
The research means doctors have "more power to predict outcome". The first benefit is expected to be at the clinical trial stage.
"It's clearly a new way of selecting the best trials for patients," said Professor Caldas. "It's not going to change the outcome for patients treated in the NHS tomorrow. But it will change the way we do clinical trials with new avenues to develop targeted treatments."
He said the new development helped scientists to understand why some women with breast cancer have a much better prognosis than others, but stressed that more research would be needed.
"This is a first, very important step," he said. "What follows is that we need to validate this as clinically useful."
Professor Caldas said that scientists now understood what tumours look like at a molecular level and will eventually know which drugs it will respond to.
He added: "The next stage is to discover how tumours in each subgroup behave - for example, do they grow or spread quickly?
"And we need to carry out more research in the laboratory and in patients to confirm the most effective treatment plan for each of the 10 types of breast cancer."
Kate Law, director of clinical and population research at Cancer Research UK, admitted that the research would not help women affected with breast cancer today, but rather future generations.
She thanked the women who had taken part in the study, all of whom had been diagnosed with breast cancer between five and 10 years ago, and said: "This is about them recognising it's their daughters and granddaughters who are going to benefit from this research.
"They are fantastically pleased and delighted to feel they are doing something positive from their disease."
Dr Kumar added: "This is going to change the way we look at breast cancer, going forward. This will, in the years to come, have a tremendous impact on the ways we think about diagnosing and treating women with breast cancer that should enable us to continue the tremendous progress we have made over the past 25 years."
The research was carried out in collaboration with the BC Cancer Agency in Vancouver, Canada, and included data collected from hospitals in London and Nottingham.
Breast cancer is now the most common cancer in the UK. Eight out of 10 women now survive breast cancer for more than five years, compared with five out of 10 women in the 1970s.
Baroness Delyth Morgan, chief executive of the Breast Cancer Campaign, said: "Breast Cancer Campaign welcomes this landmark study which could revolutionise the way breast cancer is diagnosed and treated to help the 48,000 people diagnosed with the disease every year.
"Being able to tailor treatments to the needs of individual patients is considered the holy grail for clinicians and this extensive study brings us another step further to that goal."
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