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A new breast cancer treatment strategy just got the green light. The FDA granted accelerated approval to camizestrant (Etcamah) plus a CDK4/6 inhibitor for HR+/HER2– advanced breast cancer patients who develop an ESR1 mutation during first-line therapy. Based on the phase 3 SERENA-6 trial, the approval also introduces a landmark concept: switching treatment based on molecular signals in the blood—before cancer visibly progresses.
A new breast cancer treatment strategy just got the green light
On September 4, 2026, the FDA granted accelerated approval to camizestrant (Etcamah) in combination with a CDK4/6 inhibitor (abemaciclib, palbociclib, or ribociclib) for adults with HR+/HER2– locally advanced or metastatic breast cancer that acquires an ESR1 mutation during aromatase inhibitor and CDK4/6 inhibitor therapy. The approval is based on data from the phase 3 SERENA-6 trial, which enrolled 315 patients and used serial ctDNA monitoring to detect ESR1 mutations before clinical progression — then randomized patients to either switch to camizestrant or continue their current regimen.
The results were striking: patients who switched to camizestrant saw significantly longer progression-free survival and a major delay in quality-of-life deterioration compared to those who stayed on their aromatase inhibitor. The Guardant360 CDx liquid biopsy assay serves as the companion diagnostic for this indication, and has also received CE marking in Europe.
By the numbers
Why it matters: This approval doesn't just add a new drug — it introduces a new treatment paradigm. By acting on molecular signals in the blood before tumors visibly progress, oncologists can now intervene earlier and more precisely, potentially reshaping how resistance to endocrine therapy is managed across breast cancer and beyond.
