The FDA has granted accelerated approval to Etcamah (camizestrant), used with a CDK4/6 inhibitor, for some adults with hormone receptor (HR)-positive, HER2-negative locally advanced or metastatic breast cancer. The treatment is for patients whose cancer develops an ESR1 mutation while they are receiving an aromatase inhibitor plus a CDK4/6 inhibitor, identified with an FDA-authorized test.
A new option before cancer progression
For people with HR-positive, HER2-negative advanced breast cancer, treatment often includes endocrine (hormone) therapy—such as an aromatase inhibitor—combined with a CDK4/6 inhibitor. The approved CDK4/6 inhibitors that can be used with Etcamah are:
- Abemaciclib (Verzenio)
- Palbociclib (Ibrance)
- Ribociclib (Kisqali)
The approval provides an option to switch the endocrine-therapy component from an aromatase inhibitor to camizestrant when an ESR1 mutation is detected, while continuing the CDK4/6 inhibitor. Importantly, this strategy may be considered before cancer progression is visible on scans or causes new symptoms.fda+1
ESR1 mutations are changes in the estrogen receptor gene that can develop during treatment with aromatase inhibitors. These mutations may allow cancer cells to keep using estrogen-receptor signaling to grow despite ongoing aromatase-inhibitor therapy. Camizestrant is an estrogen-receptor antagonist designed to block this pathway.
Blood testing guides treatment
The FDA also approved the Guardant360 CDx blood test as a companion diagnostic for identifying patients with ESR1-mutated breast cancer who may be candidates for Etcamah. The test looks for circulating tumor DNA (ctDNA)—small fragments of tumor DNA that can be found in a blood sample.
In the SERENA-6 study, patients underwent ctDNA testing during first-line treatment with an aromatase inhibitor and a CDK4/6 inhibitor. Participants had received that combination for at least 6 months and did not have evidence that their cancer had progressed when they entered the study. Once an ESR1 mutation was detected, patients were randomly assigned to either:
- Switch to daily camizestrant while continuing a CDK4/6 inhibitor.
- Continue their aromatase inhibitor—anastrozole or letrozole—while continuing a CDK4/6 inhibitor.
What the study found
SERENA-6 was a phase 3 clinical trial that included 315 adults with ER-positive, HER2-negative locally advanced or metastatic breast cancer and detectable ESR1 mutations.
Patients who switched to camizestrant plus a CDK4/6 inhibitor had a median progression-free survival of 16 months, compared with 9.2 months among those who continued an aromatase inhibitor plus a CDK4/6 inhibitor. This means the camizestrant strategy reduced the risk of cancer progression or death by 56% in the study, although individual results can vary.
At the time the progression-free-survival results were analyzed, overall-survival data were not yet mature. In other words, researchers did not yet have enough information to determine whether the treatment approach helps people live longer.fda
Side effects and safety
Etcamah has a boxed warning about the risk of heart-rhythm problems caused by QTc interval prolongation when it is taken with other medicines that can also prolong the QTc interval. The prescribing information also includes warnings about:
- A slow heart rate, known as bradycardia
- Possible harm to an unborn baby during pregnancy
Patients should tell their oncology team and pharmacist about every prescription medicine, over-the-counter medication, vitamin, and supplement they use. This is especially important because some medicines may affect heart rhythm or interact with cancer treatment.
Contact the cancer care team promptly for symptoms that may signal a heart-rhythm concern, such as fainting, dizziness, a fast or irregular heartbeat, chest discomfort, or unusual shortness of breath. Do not stop or change cancer medicines without discussing it with the oncology team first.
What “accelerated approval” means
Accelerated approval is an FDA pathway that can make treatments available earlier for serious conditions when study results suggest they may offer meaningful benefit. Under this pathway, the manufacturer is generally required to continue research to confirm the treatment’s clinical benefit.
For patients with eligible HR-positive, HER2-negative advanced breast cancer, the approval highlights a growing role for blood-based tumor-DNA testing. Rather than waiting for changes to appear on imaging scans, care teams may be able to identify an emerging ESR1 mutation and adjust treatment sooner. Whether this approach is appropriate depends on a patient’s cancer history, current medicines, test results, and overall health.
References
Bidard F-C, Mayer EL, Hee Park Y, et al. First-Line Camizestrant for Emerging ESR1-Mutated Advanced Breast Cancer. NEJM. Published online: June 1, 2025.
Turner N, Mayer E, Park YH, et al. Camizestrant + CDK4/6 inhibitor (CDK4/6i) for the treatment of emergent ESR1 mutations during first-line (1L) endocrine-based therapy (ET) and ahead of disease progression in patients (pts) with HR+/HER2– advanced breast cancer (ABC): Phase 3, double-blind ctDNA-guided SERENA-6 trial. J Clin Oncol. 2025;43(suppl 17):LBA4.
Bidard FC, Mayer EL, Park YH, et al. Updated results and an exploratory analysis of ESR1m circulating tumor DNA dynamics from SERENA-6, a phase 3 trial of camizestrant + CDK4/6 inhibitor for emergent ESR1m during first-line endocrine-based therapy and ahead of disease progression in patients with HR+/HER2– advanced breast cancer. Presented at: 2025 San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, TX. Abstract RF7-03.
