The U.S. Food and Drug Administration granted accelerated approval to Etcamah (camizestrant) in combination with a CDK4/6 inhibitor (abemaciclib, palbociclib, or ribociclib) for adult patients with hormone receptor‑positive (HR+), human epidermal growth factor receptor 2‑negative (HER2−), locally advanced or metastatic breast cancer. The approval applies when an ESR1 (estrogen receptor‑1) resistance mutation is detected during ongoing therapy with an aromatase inhibitor plus a CDK4/6 inhibitor, and detection is made using an FDA‑authorized test.
This approval expands treatment options for patients whose tumors acquire a specific resistance mutation during frontline endocrine therapy and provides a targeted oral therapy option to be used in combination with a CDK4/6 inhibitor under these molecularly defined circumstances.
ESR1 mutations are acquired resistance mutations that can develop in tumors during treatment with aromatase inhibitors, a common frontline endocrine therapy for locally advanced or metastatic HR+ breast cancer. At initial diagnosis of HR+ metastatic disease, fewer than 5% of patients have an ESR1 mutation; after disease progression on an aromatase inhibitor, nearly 40% of patients will have acquired this mutation.
The FDA highlighted the use of circulating tumor DNA (ctDNA) for earlier molecular detection of resistance. ctDNA consists of small fragments of tumor DNA shed into the bloodstream and can reveal resistance mutations before radiographic or clinical progression is evident. This approval represents the first FDA authorization of a cancer therapy guided by detection of a resistance mutation in ctDNA prior to imaging‑confirmed progression.
Accelerated approval of Etcamah was based on a clinical trial that evaluated switching patients to Etcamah (oral tablet) combined with a CDK4/6 inhibitor versus continuing an aromatase inhibitor combined with a CDK4/6 inhibitor. The primary basis for approval was a surrogate or intermediate endpoint measuring how long patients lived without disease worsening from the time the resistance mutation was first detected in blood.
Estimated median progression‑free survival (PFS) was 16 months in the Etcamah plus CDK4/6 inhibitor arm versus 9.2 months in the aromatase inhibitor plus CDK4/6 inhibitor arm. Because the trial endpoint measured time from molecular detection rather than traditional radiographic progression, the FDA required confirmatory trials to verify and describe the clinical benefit of intervening at the point of ctDNA‑detected mutation.
To ensure appropriate patient selection, the FDA authorized the Guardant360 CDx assay as a companion diagnostic device to identify patients whose tumors harbor ESR1 mutations for treatment with camizestrant. The companion diagnostic authorization aligns the molecular testing method with the approved indication for Etcamah.
The prescribing information for Etcamah includes a boxed warning about the risk of irregular heart rhythm when Etcamah is administered concomitantly with certain other medications. Additional warnings and precautions note the potential for an abnormally slow heart rate (bradycardia) and possible harm to an unborn baby.
Full prescribing information for Etcamah will be posted on Drugs@FDA. Clinicians should consult the official labeling for detailed contraindications, drug‑drug interaction guidance, dosing recommendations, and monitoring requirements.
The accelerated approval pathway permits earlier approval of therapies for serious conditions that address unmet medical needs based on surrogate or intermediate clinical endpoints. The FDA publicly emphasized that this approval is the first to be guided by detection of a resistance mutation in ctDNA prior to imaging‑detected progression. The Oncologic Drugs Advisory Committee reviewed the application on April 30, 2026.
The accelerated approval for Etcamah (camizestrant) was granted to AstraZeneca. The FDA noted the agency’s commitment to advancing medical innovation and making new targeted therapies available to patients with evolving resistance profiles.
Because accelerated approval was granted on the basis of a surrogate endpoint—the time patients lived without disease worsening measured from the point of ctDNA detection—the FDA required confirmatory studies to verify and describe clinical benefit. The agency stated that it is not yet confirmed whether intervening at the time a resistance mutation is detected in blood, rather than at conventional clinical or radiographic progression, translates into a meaningful long‑term benefit for patients.
Sponsors and investigators will need to complete the required confirmatory trials to confirm clinical outcomes. The FDA will update labeling and regulatory status based on results from those studies. Meanwhile, the Guardant360 CDx has been authorized as the companion diagnostic to identify eligible patients, and clinicians should follow the approved indication and prescribing information when considering Etcamah for treatment.