SERENA-6 Shows Benefit of Starting Camizestrant Early
- SERENA-6 shows that switching from first-line aromatase inhibitor to the oral SERD camizestrant at the time an ESR1 mutation is detected—before clinical progression, with continuation of CDK4/6 inhibitor, significantly prolongs PFS (~9 → ~16 months; ~55–60% risk reduction) and improves quality of life, supporting proactive management of endocrine resistance.
- Camizestrant plus continued CDK4/6 inhibition was generally well-tolerated, with most side effects driven by the CDK4/6 inhibitor; camizestrant-specific toxicities were mild and manageable, reinforcing the appeal of oral SERDs in routine care.
- Greater maturity of the data, in addition to, long-term tolerability, regulatory approval, and cost-effectiveness will influence how broadly this approach can be implemented in clinical practice.
Approximately 40% of advanced HR+/HER2- breast cancer patients with documented progression while on first-line therapy, generally a CDK4/6 inhibitor plus aromatase inhibitor, will develop an ESR1 (Estrogen Receptor 1) mutation. These ESR1 mutations lead to constitutive activity independent of estrogen levels but remain sensitive to inhibition with SERDs (Selective Estrogen Receptor Degraders). Camizestrant is a novel next-generation oral SERD recently evaluated in the randomized double-blinded SERENA-6 Trial.
A major advantage of the SERENA-6 trial is its innovative design, which validates liquid biopsy-guided treatment adaptation before clinical progression, representing a shift toward proactive management of emerging endocrine resistance. “These data supports that, switching to camizestrant at time of emergence of an ESR1 mutation, but in advance of clinical progression, is having a meaningful impact not only on prolonging progression-free survival, but also in helping patients feel better and be able to function better in their daily lives,” explains Dr. Erica Mayer, a Medical Oncologist at the Dana Farber Cancer Institute and a lead US SERENA-6 investigator.
Camizestrant is “the first oral SERD to demonstrate clinical benefit in the first-line treatment of HR+/HER2− breast cancer. The totality of the efficacy data (PFS, PFS2, chemotherapy-free survival), the highly significant — and rarely observed — quality-of-life benefit, and the safety profile all support the concept that targeting ESR1 mutations as soon as they emerge, and before clinical progression, is the optimal timing,” adds Dr. Francois-Clement Bidard, an oncologist at the Institut Curie and lead global SERENA-6 investigator.
Key limitations include immature overall survival data, reliance on frequent ctDNA monitoring (which may not yet be universally available), and applicability limited to patients who develop detectable ESR1 mutations rather than all endocrine-resistant disease. Additionally, long-term tolerability and cost-effectiveness of routine molecular surveillance remain open questions.
While there are several oral SERDs currently either on the market or in development, the question of the superiority of one oral SERD of another remains an open question. Dr. Mayer explains “there is no clinical data available comparing these drugs head to head…There are some subtle toxicity differences among the agents, but no major issues that would appear to be a high level differentiator among the different drugs.”
On whether oral SERDS displace the existing endocrine agents, Dr. Mayer is optimistic. “We definitely have a number of signals suggesting oral SERDs perhaps are better tolerated than some of our existing agents. So it’s going to be very exciting,” she explains.
General Eligibility Criteria
- Advanced (locally advanced or metastatic) HR+ / HER2- breast cancer not amenable to curative therapy.
- Currently on first-line endocrine therapy with an AI plus a CDK4/6 inhibitor for at least 6 months.
- Detection of an ESR1 mutation in ctDNA without radiological disease progression at routine imaging.
- Histologically confirmed disease and met other standard clinical and lab criteria for trial participation.
Randomization & Study Design
Eligible patients with emergent ESR1 mutations were randomized 1:1 to:
• Switch from AI to Camizestrant + continue same CDK4/6 inhibitor with addition of a placebo, or
• Continue AI + same CDK4/6 inhibitor and addition of a placebo.
Both arms were double-blind with matching placebos to maintain blinding.
Primary & Secondary Endpoints
The primary endpoint of the trial was progression-free survival (PFS) from the time of randomization. Key secondary endpoints included overall survival, PFS2, safety, and quality-of-life measures.
The trial demonstrated a statistically significant and clinically meaningful improvement in PFS with camizestrant. Switching therapy at the time of molecular resistance reduced the risk of progression or death by approximately 56% compared with continuing AI therapy, with median PFS extending from roughly 9 months to 16 months. Benefit was consistent across CDK4/6 inhibitor subgroups. Overall survival data remain immature, but early trends favor the camizestrant arm.
Side Effects
In terms of safety, camizestrant was generally well tolerated. Most adverse events were driven by the background CDK4/6 inhibitor, including neutropenia and anemia. Camizestrant-specific effects included low-grade visual symptoms (photopsia) and mild gastrointestinal effects, which were typically reversible. Treatment discontinuation rates were low and comparable between arms, with no new major safety signals.
“In general, oral SERDs are very well tolerated, which is wonderful from a patient point of view and may lead to greater adherence and greater efficacy as well,” Dr. Mayer adds.
