AstraZeneca (NYSE: AZN) reported updated results from its Phase III SERENA-6 trial showing that camizestrant combined with a CDK4/6 inhibitor reduced the risk of disease progression or death by 55% in patients with advanced hormone receptor-positive breast cancer who developed ESR1 tumor mutations.

The trial evaluated switching to camizestrant plus a CDK4/6 inhibitor versus continuing standard treatment with an aromatase inhibitor plus a CDK4/6 inhibitor. Median progression-free survival was 16.8 months for the camizestrant combination compared with 9.2 months for the standard treatment.

For the secondary endpoint measuring durability beyond first progression, the camizestrant combination reduced the risk of second disease progression or death by 37% compared to standard treatment. Median second progression-free survival was 25.7 months versus 19.1 months.

The study showed substantial differences in circulating tumor DNA levels. Patients receiving camizestrant had a median 99% reduction in total circulating tumor DNA by week 8, with 51% achieving complete clearance. Patients on standard treatment showed a median 64% increase in circulating tumor DNA, with 1.9% achieving clearance.

The trial enrolled 315 patients with hormone receptor-positive, HER2-negative advanced breast cancer who were receiving first-line treatment with an aromatase inhibitor plus a CDK4/6 inhibitor. The study used blood tests to detect ESR1 mutations that signal emerging resistance to endocrine therapy.

Camizestrant is approved in the United Arab Emirates and Saudi Arabia. The European Medicines Agency recently adopted a positive opinion recommending approval in the European Union. The U.S. Food and Drug Administration extended its review timeline to consider the updated trial data.

The results were presented at the American Society of Clinical Oncology Annual Meeting and build on data previously published in The New England Journal of Medicine.