Key Findings from the SERENA-6 Phase III Trial
- Study Design
The SERENA-6 trial enrolled 3,256 patients receiving first-line therapy with an aromatase inhibitor (AI) plus a CDK4/6 inhibitor. Patients were monitored via ctDNA every 2–3 months to detect emerging ESR1 mutations prior to radiologic progression. Of these, 315 patients developed ESR1 mutations and were randomized: one group switched to camizestrant (75 mg daily) plus continued CDK4/6 inhibition (n=157); the other continued AI + CDK4/6 with placebo (n=158) - Progression-Free Survival (PFS)
- Camizestrant arm: median PFS of 16.0 months (95% CI 12.7–18.2)
- Control arm: median PFS of 9.2 months (95% CI 7.2–9.5)
- Hazard ratio for progression/death: 0.44, reflecting a 56% reduction in risk (P < 0.0001)
- Quality of Life (QoL)
- Time to deterioration in global health status: 23.0 months with camizestrant vs 6.4 months with AI (HR = 0.53)
- Safety Profile
- Treatment discontinuation due to AEs was low: 1.3% (camizestrant) vs 1.9% (AI)
- Grade 3 or higher adverse events were more frequent with camizestrant (60.0% vs 45.8%), largely hematologic toxicities like neutropenia; other events such as photopsia were more common but generally mild and manageable
- Regulatory Status
Based on these results, the FDA granted Breakthrough Therapy designation to camizestrant (in combination with a CDK4/6 inhibitor) for HR-positive, HER2-negative advanced breast cancer when an ESR1 mutation emerges during first-line endocrine therapy - Potential Clinical Impact
Experts and media reports suggest that this approach—using a liquid biopsy to detect resistance early and switching to camizestrant—could establish a new precision oncology paradigm and change first-line treatment in practice