By VETTAPHARMA reporter – Derek Roche: AstraZeneca reported positive results from the Phase III SERENA-6 trial showing that switching to camizestrant in combination with a CDK4/6 inhibitor significantly delayed disease progression in patients with hormone receptor (HR)-positive, HER2-negative advanced breast cancer harboring an emerging ESR1 mutation. The findings were presented during a plenary session at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting and simultaneously published in The New England Journal of Medicine.
The trial met its primary endpoint, demonstrating a 56% reduction in the risk of disease progression or death compared with continuing standard-of-care aromatase inhibitor therapy plus a CDK4/6 inhibitor (hazard ratio [HR] 0.44; 95% confidence interval [CI] 0.31–0.60; p<0.00001). Median progression-free survival was 16.0 months for patients switched to camizestrant compared with 9.2 months in the comparator arm.
SERENA-6 is a global, double-blind, randomized Phase III trial evaluating a circulating tumor DNA (ctDNA)-guided treatment strategy in patients receiving first-line aromatase inhibitor therapy plus a CDK4/6 inhibitor. The study enrolled 3,256 patients who underwent regular ctDNA monitoring, with 315 patients identified as having an emerging ESR1 mutation and subsequently randomized to either switch to camizestrant or continue aromatase inhibitor therapy while maintaining the same CDK4/6 inhibitor.
The study assessed whether early intervention at the molecular progression stage—before radiographic disease progression becomes apparent—could improve outcomes. ESR1 mutations are a recognized mechanism of endocrine resistance and frequently emerge during treatment with aromatase inhibitors in advanced breast cancer.
Secondary endpoints also favored the camizestrant strategy. Time to second disease progression or death was improved by 48% (HR 0.52; 95% CI 0.33–0.81), while progression-free survival 2 showed a 47% reduction in risk (HR 0.53; 95% CI 0.33–0.84). The safety profile of camizestrant was consistent with previous studies, and no new safety signals were identified.
HR-positive, HER2-negative breast cancer represents the most common subtype of breast cancer. Despite advances in endocrine therapy and CDK4/6 inhibitors, acquired resistance remains a major challenge, with ESR1 mutations frequently emerging during treatment and contributing to disease progression.
For patients, the results suggest that monitoring for ESR1 mutations using ctDNA testing and switching therapy before clinical progression may substantially extend disease control. The approach could enable earlier intervention against endocrine resistance and potentially delay disease worsening.
Commercially, the findings position camizestrant as a potential first-in-class endocrine therapy strategy guided by molecular monitoring. Positive Phase III data may support future regulatory submissions and strengthen AstraZeneca’s breast cancer portfolio by expanding treatment options in HR-positive metastatic disease.
Quick FAQs
What Is the Drug/Product/Asset?
Camizestrant is AstraZeneca’s investigational next-generation oral selective estrogen receptor degrader (SERD) being developed for HR-positive, HER2-negative breast cancer.
What Did AstraZeneca Present at ASCO?
AstraZeneca presented Phase III SERENA-6 data showing that switching patients with emerging ESR1 mutations from aromatase inhibitor therapy to camizestrant significantly delayed disease progression.
What Is the Study/Trial?
SERENA-6 is a global Phase III, double-blind, randomized trial evaluating a ctDNA-guided treatment strategy in patients with HR-positive, HER2-negative advanced breast cancer receiving first-line aromatase inhibitor therapy plus a CDK4/6 inhibitor. A total of 3,256 patients were monitored, with 315 ESR1-mutated patients randomized.
What Is the Disease Condition?
HR-positive, HER2-negative breast cancer is the most common form of breast cancer. ESR1 mutations can emerge during endocrine therapy and contribute to treatment resistance and disease progression.
What Were the Key Results?
Camizestrant reduced the risk of disease progression or death by 56% versus continued aromatase inhibitor therapy (HR 0.44; p<0.00001). Median progression-free survival was 16.0 months compared with 9.2 months. Improvements were also observed in key secondary endpoints.
Why Is This Important?
The findings support a ctDNA-guided treatment approach that identifies endocrine resistance before clinical progression occurs. This strategy may help patients remain progression-free longer while creating a potential new treatment paradigm in advanced HR-positive breast cancer.
