A new drug can help stop certain breast cancer tumours before they grow, experts say.
A trial called Serena-6 shows that camizestrant stops cancer cells from using hormones to grow, which helps patients stay well longer and delays the need for chemotherapy.
It is the first worldwide study to show that using blood tests to find early signs of cancer resistance to treatment helps patients, scientists say.
The study looked at patients who had hormone-positive, HER2-negative breast cancer, which is about 70% of cases.
Results showed patients given camizestrant reduced their chances of cancer progression by 56%, compared with just standard therapies.
Doctors used a simple blood test to spot changes in the cancer’s DNA that show whether current treatments might soon stop working.
When they found these signs, some patients were given camizestrant, while others stayed on their usual treatment.
Those on camizestrant had their cancer stay the same and not get worse for much longer, 16 months on average, compared with about nine months for the others.
The drug was safe for most patients but 1% stopped taking it because of side effects.
More than 3,000 patients from 23 countries took part in the study, which was funded by AstraZeneca and co-led by researchers at The Institute of Cancer Research in London.
Co-principal investigator Professor Nick Turner, group leader in molecular oncology at The Institute of Cancer Research, London, said the drug is “a pivotal moment in breast cancer care”.
Professor Kristian Helin, chief executive of The Institute of Cancer Research said: “The results of the Serena-6 trial represent more than a clinical milestone, they represent a transformational shift in how we approach precision medicine.”
About 55,000 women are diagnosed with breast cancer in the UK every year and 11,500 will die from the disease, The Institute of Cancer Research said.
The Serena-6 trial results were to be presented at the American Society of Clinical Oncology (ASCO) annual meeting in Chicago on Sunday.
Dr Catherine Elliott, director of research at Cancer Research UK, said: “This study is a clear example of how blood tests are starting to transform cancer treatment.
“By tracking tiny traces of tumour DNA in the blood, researchers were able to spot early signs of treatment resistance and switch therapies before cancer had a chance to grow.
“It shows how circulating tumour DNA, or ctDNA, could help doctors make smarter, more timely treatment decisions.
“This approach could become an important part of how we personalise care for people with advanced breast cancer.”
