The study suggests that adding progesterone - a cheap, safe and widely available drug - to their treatment could help around half of breast cancer patients live longer.
The international team of researchers came to this conclusion after examining breast cancer cells that had been "rescued" for research.
They found that progesterone appears to slow cancer cell growth by changing estrogen receptor interaction with DNA.
Not all breast cancers are hormone-driven. Around 75% of patients with breast cancer are positive for estrogen receptors (ER+) and around 75% of those are positive for progesterone receptors (PR+), so the researchers suggest their findings could benefit around half of breast cancer patients.
Patients with ER+ breast cancers are often treated with drugs like tamoxifen to block estrogen receptors. The study suggests that adding progesterone - a cheap, safe and widely available drug - to their treatment could help them live longer.
'Strong case for clinical trials'
For the study, the researchers used advanced DNA reading technology to locate where the estrogen receptor attaches to DNA to switch on genes to drive cancer cell growth.
They then grew breast cancer cells with and without progesterone and found when the progesterone receptor is activated, it redirects the estrogen receptor to different DNA regions. This switches on a different set of genes that slows down cell growth.
However, the research is still in its early days - what works in cells in the lab does not necessarily work in live patients.
Nevertheless, the researchers believe their findings are strong enough to start thinking about testing in humans, as senior author Dr. Jason Carroll, of Cambridge University in the UK, explains:
"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."
The discovery was made possible because of a new technique developed at the University of Adelaide in Australia - one of the centers participating in the study. The technique allows breast cancer cells from volunteer patients to be "rescued" for research.
Together with the advanced DNA reading technology developed at Cambridge, the technique enabled the researchers to observe hormone regulation and its effects on breast cancer cells in a new way, as Dr. Carroll explains:
"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."
Cancer Research UK, the European Research Council, the National Health and Medical Research Council of Australia, Cancer Australia and the National Breast Cancer Foundation funded the research.
Meanwhile, Medical News Today recently learned of another study published in Molecular Cell where researchers found how a small molecule helps the BRCA gene resist cancer treatment. The Yale School of Medicine team says their findings could lead to treatments that decrease drug resistance in cancers involving BRCA genes.