FDA Grants Accelerated Approval to Camizestrant for ESR1-Mutated Breast Cancer

On September 4, 2026, the US Food and Drug Administration (FDA) granted accelerated approval to camizestrant (Etcamah, AstraZeneca), an oral estrogen receptor antagonist, for adults with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative locally advanced or metastatic breast cancer. The camizestrant breast cancer approval is granted in combination with a CDK4/6 inhibitor (abemaciclib, palbociclib, or ribociclib).

The indication is limited to patients whose tumors carry an estrogen receptor-1 (ESR1) mutation, detected during aromatase inhibitor and CDK4/6 inhibitor therapy using an FDA-authorized test. The FDA also approved the Guardant360 CDx assay as a companion diagnostic to identify patients with ESR1 mutations who are eligible for camizestrant.

Camizestrant breast cancer: SERENA-6 results

Efficacy was evaluated in SERENA-6 (NCT04964934), a randomized, double-blind, placebo-controlled, multicenter trial. The study compared switching to camizestrant plus a CDK4/6 inhibitor against continuing an aromatase inhibitor (AI) plus a CDK4/6 inhibitor in adults with ER-positive, HER2-negative locally advanced or metastatic breast cancer and detectable ESR1 mutations.

ESR1 status was assessed by blood circulating tumor DNA (ctDNA) testing with the Guardant360 CDx assay during first-line treatment. All patients had to be receiving an AI plus a CDK4/6 inhibitor for at least 6 months as their initial endocrine-based treatment, with no disease progression. A total of 315 patients were randomized 1:1 to camizestrant once daily plus a CDK4/6 inhibitor, or an AI (anastrozole or letrozole) orally once daily plus a CDK4/6 inhibitor.

The primary outcome was investigator-assessed progression-free survival (PFS) per RECIST v1.1. Median PFS was 16 months (95% CI: 12.7, 18.2) in the camizestrant arm versus 9.2 months (95% CI: 7.2, 9.5) in the AI arm. The hazard ratio was 0.44 (95% CI: 0.31, 0.60; p < 0.00001). Overall survival data were not mature at the time of the PFS analysis.

Safety

The prescribing information carries a boxed warning for the risk of arrhythmia due to QTc interval prolongation when camizestrant is used with other QTc-prolonging drugs. Warnings and precautions also cover bradycardia and embryo-fetal toxicity.

Dosing

The recommended dose is 75 mg orally once daily, with or without food, until disease progression or unacceptable toxicity. The CDK4/6 inhibitor continues at the same dose as when the mutation was detected.

Accelerated approval and global review

The approval is based on progression-free survival measured from detection of the mutation. Continued approval may depend on verification of clinical benefit in a confirmatory trial. This review was conducted under Project Orbis, with the FDA collaborating with Australia’s Therapeutic Goods Administration (TGA), Brazil’s ANVISA, Health Canada, Singapore’s Health Sciences Authority (HSA), and Switzerland’s Swissmedic. The application received standard review, and camizestrant had breakthrough therapy designation. The application was discussed at an Oncology Drugs Advisory Committee meeting.

Source: US Food and Drug Administration