Dr J?©z?©quel continued: "The UBE2C protein appears to be linked to a process called the proteasome system, which when it goes wrong, can drive this type of cancer. So, we believe that the chemotherapy drug bortezomib (Velcade), which is designed to block proteasome activity, could work against this form of the disease.

"If this is shown to work in clinical trials, it could open the door to more effective treatments for a group of patients who are served less well by existing therapies."

Dr Lesley Walker, director of cancer information at Cancer Research UK, said: "We no longer see people with breast cancer as belonging to a single group because we now know there are many different forms of the disease. Personalising treatments in this way enables doctors to decide what treatment is likely to have the best effect to improve survival and avoid unnecessary treatment.

"The next stage will be to see if this protein can be used as a predictive biomarker by doctors to decide how best to treat this group of patients and to see how useful it will be."

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