WILMINGTON, DE — AstraZeneca reported updated Phase III trial results showing its investigational breast cancer therapy camizestrant extended the time patients lived without disease progression and delayed the need for additional treatment, potentially strengthening the drug’s regulatory and commercial prospects in a competitive oncology market.
The findings, presented at the American Society of Clinical Oncology annual meeting in Chicago, build on earlier results from the SERENA-6 trial and come as regulators in the United States, Japan and other markets review applications for the treatment.
The study evaluated patients with hormone receptor-positive, HER2-negative advanced breast cancer whose tumors developed ESR1 mutations during first-line treatment. Researchers tested whether switching patients to camizestrant while continuing an existing CDK4/6 inhibitor could improve outcomes compared with remaining on standard endocrine therapy.
According to AstraZeneca, patients who switched to camizestrant plus a CDK4/6 inhibitor experienced a median progression-free survival of 16.8 months, compared with 9.2 months for patients who remained on standard treatment. The results translated into a 55% reduction in the risk of disease progression or death during the study period.
Updated data also showed improvement in second progression-free survival, a measure designed to evaluate whether treatment benefits persist beyond the first disease progression and subsequent therapies. AstraZeneca said the camizestrant regimen reduced the risk of second disease progression or death by 37%, with median second progression-free survival of 25.7 months versus 19.1 months for the comparison group.
The results could be significant because treatment resistance remains a major challenge in hormone receptor-positive breast cancer, the most common subtype of the disease.
Researchers also reported substantial differences in circulating tumor DNA, or ctDNA, a biomarker increasingly used to monitor treatment response and disease burden. Patients receiving camizestrant achieved a median 99% reduction in total ctDNA by week eight, while patients remaining on standard treatment experienced a median 64% increase.
More than half of patients receiving camizestrant achieved complete ctDNA clearance compared with 1.9% of patients in the standard-care group, according to the company.
François-Clément Bidard, a medical oncology professor at Institut Curie and co-principal investigator of the study, said the findings support earlier intervention when ESR1 mutations emerge.
“Once the disease progresses, it becomes harder to treat and outcomes worsen,” Bidard said. “The updated SERENA-6 results support the paradigm of switching to a camizestrant-based combination in the first-line setting upon emergence of an ESR1 mutation.”
The study also found that patients receiving camizestrant went longer before requiring chemotherapy or antibody-drug conjugate treatment. Median chemotherapy- or antibody-drug-conjugate-free survival was 22.6 months compared with 18.7 months in the standard-treatment group.
An interim analysis of overall survival showed a numerical trend favoring camizestrant, though the data are not yet mature enough to determine a statistically significant survival benefit. The trial will continue until final overall survival results become available.
AstraZeneca said no new safety concerns were identified, and discontinuation rates were low and similar between the treatment groups.
Camizestrant has already received approval in the United Arab Emirates and Saudi Arabia. The European Medicines Agency’s Committee for Medicinal Products for Human Use recently issued a positive opinion recommending approval in the European Union, while the U.S. Food and Drug Administration is continuing its review after extending its decision timeline to evaluate the updated trial data.
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