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"
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 classificatio. The potential here is huge and it could have a transformative role in breast cancer care. However, we are a long way from using the new definitions in hospitals and the immediate impact on patients will be limited.
There are clear survival differences among the 10 categories. Clusters two and five seem to have a 15-year survival of around 40%. Clusters three and four have around 75% survival over the same period. This could help better inform patients.
In terms of treatments, there is bad news. There is a targeted therapy for just one of the 10 breast cancers groups. That is Herceptin, which is already used in a targeted group of patients. Other groups will still have "standard" therapies such as chemotherapy or radiotherapy.
The hope is that by identifying the 10 breast cancers it will be possible for researchers to design drugs for each one, but that is still a work in progress.
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