On September 4, 2026, the U.S. Food and Drug Administration (FDA) granted accelerated approval to camizestrant (Etcamah), an estrogen receptor antagonist, in combination with a CDK4/6 inhibitor (abemaciclib, palbociclib, or ribociclib) for adults with hormone receptor (HR)-positive, HER2-negative locally advanced or metastatic breast cancer upon detection of ESR1 mutation during aromatase inhibitor and CDK4/6 inhibitor therapy, based on an FDA-authorized test.
FDA also approved the Guardant360 CDx assay as a companion diagnostic device to identify patients with breast cancer with ESR1 mutations for treatment with camizestrant.
Efficacy and Safety
Efficacy was evaluated in SERENA-6 (NCT04964934), a randomized, double-blind, placebo-controlled, multicenter trial to assess switching to camizestrant in combination with a CDK4/6 inhibitor vs continuing an aromatase inhibitor (AI) in combination with a CDK4/6 inhibitor in adult patients with ER-positive, HER2-negative locally advanced or metastatic breast cancer with detectable ESR1 mutations.
The ESR1 mutation status was assessed by blood circulating tumor DNA (ctDNA) testing using the Guardant360 CDx assay during first-line treatment with an AI and a CDK4/6 inhibitor.
All patients were required to be currently receiving treatment with an AI in combination with a CDK4/6 inhibitor for ≥ 6 months as the initial endocrine-based treatment with no evidence of disease progression as per investigator assessment. A total of 315 patients were randomly assigned 1:1 to receive either camizestrant once-daily in combination with a CDK4/6 inhibitor or AI (anastrozole or letrozole) orally once-daily in combination with a CDK4/6 inhibitor.
The primary efficacy outcome measure was investigator-assessed progression-free survival per RECIST v1.1. An additional efficacy outcome measure included overall survival. Median progression-free survival was 16 months (95% confidence interval [CI] = 12.7–18.2) in the camizestrant and CDK4/6 inhibitor arm and 9.2 months (95% CI = 7.2–9.5) in the AI and CDK4/6 inhibitor arm (hazard ratio [HR] = 0.44; 95% CI = 0.31–0.60; P < .00001). At the time of the progression-free survival analysis, overall survival data were not mature.
The prescribing information includes a boxed warning for the risk of arrhythmia due to QTc interval prolongation when concomitantly used with QTc interval–prolonging drugs, as well as warnings and precautions for bradycardia and embryo-fetal toxicity.
Recommended Dosage
The recommended camizestrant dose is 75 mg orally once-daily, with or without food, until disease progression or unacceptable toxicity. Camizestrant should be administered in combination with a CDK4/6 inhibitor (abemaciclib, palbociclib, or ribociclib). Continue the CDK4/6 inhibitor at the same dosage as when the ESR1 mutation was detected. Refer to the prescribing information of the CDK4/6 inhibitor for additional dosing information.
Camizestrant in combination with a CDK4/6 inhibitor (abemaciclib, palbociclib, or ribociclib) is being granted accelerated approval based on progression-free survival measured from detection of ESR1 mutation. Continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial.
