Around half of all breast cancer patients could one day benefit from having the cheap and widely-available female hormone progesterone added to their treatment, according to a paper by UK researchers published in Nature. 

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 team. Tumors fueled by the female hormone oestrogen are treated with drugs like tamoxifen to block estrogen receptors, which cause cancer cells to grow. Women whose tumors 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 estrogen receptor in breast cancer cells to change their behaviour, ultimately slowing down tumor 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 estrogen receptor, which could improve treatment for the majority of hormone-driven breast cancers."