Australian researchers have discovered a key factor explaining the lack of effectiveness of some breast cancer treatments.
Associate Professor Chris Ormandy from Sydney's Garvan Institute says a protein he has been studying for a decade plays a critical role in the development of breast cancer.
He says the protein, known as ELF5, makes breast cancer tumours more aggressive and resistant to treatment.
Professor Ormandy says the new research explains why many breast cancer patients stop responding to commonly-used anti-oestrogen treatments.
He says the protein can make tumours more aggressive.
"Unfortunately a large number of those women, approximately about a half of them, will at some point experience insensitivity to the anti-oestrogen treatment that they've been put on and their tumour will progress," he said.
"What we've found is that in tissue culture models of breast cancers that have been made to become insensitive to anti-oestrogen treatment, that the levels of [ELF5] rise dramatically in those cells.
"They've developed a way of stepping around the anti-oestrogen treatment by increasing their levels of ELF5."
Professor Ormandy says it may be many years before the finding leads to new drugs to treat breast cancer, but the discovery opens a whole new avenue of therapeutic options.
"We can now set about trying to develop therapies that will target ELF5 in a way that will either prevent the acquisition of insensitivity to anti-oestrogens or which will enable, or may enable us to treat tumours once they have become insensitive to anti-oestrogens by targeting ELF5," he said.
The work is being published in the online journal PLOS Biology.