What we currently call breast cancer should be thought of as 10 completely separate diseases, according to an international study which has been described as a “landmark”.
The categories could improve treatment by tailoring drugs for a patient’s exact type of breast cancer and help predict survival more accurately.
The study in Nature analysed breast cancers from 2,000 women.
It will take at least three years for the findings to be used in hospitals.
Researchers compared breast cancer to a map of the world. They said tests currently used in hospitals were quite broad, splitting breast cancer up into the equivalent of continents.
The latest findings give the breast cancer map far more detail, allowing you to find individual “countries”.
“Breast cancer is not one disease, but 10 different diseases,” said lead researcher Prof Carlos Caldas.
He added: “Our results will pave the way for doctors in the future to diagnose the type of breast cancer a woman has, the types of drugs that will work and those that won’t, in a much more precise way than is currently possible.”
At the moment, breast cancers are classified by what they look like under the microscope and tests for “markers” on the tumours.
Those with “oestrogen receptors” should respond to hormone therapies such as tamoxifen; those with a “Her2 receptor” can be treated with Herceptin.
The vast majority of breast cancers, more than 70%, should respond to hormone therapies. However, their reaction to treatment varies wildly. Prof Caldas said: “Some do well, some do horribly. Clearly we need better classification.”
His team looked at frozen breast cancer samples from 2,000 women at hospitals in the UK and Canada.
They looked in huge detail at the genetics of the tumour cells – which genes had been mutated, which genes were working in overdrive, which were being shut down.
The study, by researchers in the UK and Canada, showed that all the different ways the cells changed when they became cancerous could be grouped into 10 different categories – named IntClust one to 10.
Prof Caldas said this was a “completely new way of looking at breast cancer”.
The study was funded by Cancer Research UK. Its chief executive, Dr Harpal Kumar, said: “This is the largest ever study looking in detail at the genetics of breast tumours.
“This will change the way we look at breast cancer, it will have an enormous impact in the years to come in diagnosing and treating breast cancer.
“We think this is a landmark study.”
He said the charity would begin using the new criteria in clinical trials it funded.
Outside of trials for new cancer drugs, the new breast cancer rulebook could take some time to directly benefit patients.
The researchers need to prove that the 10 classifications actually provide any benefit to people with breast cancer, before they can be used by doctors.
That process is expected to take three to five years.
The chief executive of the Breast Cancer Campaign, Baroness Delyth Morgan, said the study could “revolutionise the way breast cancer is diagnosed and treated”.
“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.”
A Department of Health spokesperson said: “We are always looking at new ways to improve outcomes for cancer patients and that is why we are investing more than £750m to make sure people are diagnosed with cancer earlier and have better access to the latest treatments.
“We look forward to seeing the future results of this ongoing work and will continue to work with Cancer Research UK to find the best possible way to improve outcomes for people with breast cancer.”