Experts believe breast cancers that do not respond to hormone therapies could be treated by targeting a protein
Lethal breast cancers could be treated by targeting a protein found in cell nuclei, scientists believe.
An experimental drug that switches off the protein has already been shown to prevent tumour growth in the laboratory.
The discovery opens the door to new ways of tackling aggressive breast cancers that do not respond to hormone therapies.
About three quarters of breast tumours are driven by the female sex hormone oestrogen. They can often be treated with therapies such as tamoxifen, which blocks the effects of the hormone.
But 25% of breast cancers are not fuelled by oestrogen, and will not respond to tamoxifen or similar hormone treatments. These "oestrogen-negative" cancers tend to be the most aggressive and deadly.
The newly identified receptor protein ERRalpha controls genes involved in energy metabolism.
A genetic analysis of 800 breast tumours found an association between the protein's activity and the aggressiveness of oestrogen-negative cancers.
"When that ERRalpha receptor is active the outcome of these patients is much, much worse," said study leader Dr Donald McDonnell, from Duke University Medical Centre in the US.
The research, published in the journal Cancer Cell, suggests ERRalpha triggers tumour growth after receiving signals from two other proteins, HER2 and IGF-1R. Both are receptors that respond to stimuli from growth hormones.
As a result, ERRalpha is active in all breast cancer tumours where either HER2 or IGF-1R is also active. This most often occurs in oestrogen-negative cancers.