ASCO 2025: camizestrant regimen could target breast tumors before progression
Combination treatment involving camizestrant can cut the chances of breast cancer progression for certain breast cancer patients by over 50%.
High-level results from the SERENA-6 trial, a study led by researchers at the Institute of Cancer Research (London, UK), The Royal Marsden NHS Foundation Trust (London, UK) and the Institut Curie (Paris, France), have demonstrated that a combination therapy involving the drug camizestrant can treat emerging breast tumors, months before they progress. These results, presented at the ASCO Annual Meeting (May 30–June 3, IL, USA), highlighted the benefits of this potential new treatment strategy and ctDNA in guiding treatment decisions during endocrine resistance.
While at the time of diagnosis, mutations in the ESR1 gene are rare, they are a frequent cause of resistance and can emerge in 40% of HR+, HER2-negative breast cancer patients who are undergoing the typical first-line therapy approach of a CDK4/6 inhibitor drug plus an aromatase inhibitor.
Camizestrant, a “next-generation” oral selective estrogen receptor degrader (SERD), works by blocking and breaking down estrogen receptors in breast cancer cells, reducing the growth and spread of cancer, therefore making it a potential treatment option for patients with HR+, HER2-negative ESR1-mutated breast cancer. The SERENA-6 Phase III trial investigated if switching from an aromatase inhibitor to camizestrant in combination with the same CDK4/6 inhibitor could extend the benefit of first-line treatment in patients with emerging ESR1 mutations.
SERENA-6 is the first global trial to use a ctDNA-guided approach to detect endocrine resistance during routine scans in order to switch treatment before clinical progression signs appear.
In the study, 315 HR+, HER2-negative advanced breast cancer patients who had been on first-line therapy for at least 6 months, and who tested positive for ESR1 mutations, were randomized into the study. Half of the patients were given camizestrant alongside their CDK4/6 inhibitor, plus a dummy pill instead of their aromatase inhibitor. The other half of the patients continued their aromatase inhibitor and CDK4/6 inhibitor, plus a dummy pill instead of camizestrant.
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The results of the study revealed that combination therapy with camizestrant reduced the risk of breast cancer progression or death by 56%, with a median progression-free survival of 16 months. On the other hand, patients continuing their first-line therapy had a median progression-free survival of 9.2 months.
Further to this, the results revealed that camizestrant was well-tolerated and reduced the risk of deterioration in a patient’s general health and quality of life by 47% compared to patients who continued their first-line treatment.
“This is a pivotal moment in breast cancer care. These results demonstrate that using liquid biopsy blood tests to spot emerging resistance in tumors, before they start to grow and make the patient unwell, can guide early intervention with camizestrant to delay disease progression in patients with ESR1 mutations,” commented Nick Turner (ICR & Royal Marsden).
Further trials investigating camizestrant in broader first-line populations from the start of their treatment, as well as in early breast cancer settings, are now being conducted.