Women whose tumours have progesterone receptors as well are known to have a better outlook. But for decades scientists have been unable to pinpoint why.
Scientists at Cancer Research UK's Cambridge Research Institute and the University of Adelaide revealed how the progesterone receptor 'talks to' the oestrogen receptor in breast cancer cells to change their behaviour, ultimately slowing down tumour growth.
Cancer Research UK's Dr Jason Carroll, who led the study with Professor Wayne Tilley at the University of Adelaide in Australia, said: "We've used cutting-edge technology to tease out the crucial role that progesterone receptors play in breast cancer - a mystery that has baffled scientists for many years.
"This important laboratory research helps explain why some breast cancer patients have a better outlook. Crucially, it provides a strong case for a clinical trial to investigate the potential benefit of adding progesterone to drugs that target the oestrogen receptor, which could improve treatment for the majority of hormone-driven breast cancers."
There are around 50,000 new cases of breast cancer each year in the UK and around half could potentially benefit from this finding, according to the researchers.
Dr Emma Smith, senior science communication officer at Cancer Research UK, said: "This exciting study in cells shows how a cheap, safe, and widely available drug could potentially improve treatment for around half of all breast cancer patients. Thanks to research, almost 70 per cent of women now survive breast cancer beyond 20 years - but so much more must be done and we won't stop until we find cures for all forms of the disease."
Mohammed H. et al. Progesterone receptor modulates estrogen receptor-α action in breast cancer (link is external), Nature (2015), doi:10.1038/nature14583.