FDA approves Guardant360 CDx for ESR1 mutation testing in breast cancer

Guardant Health has received U.S. Food and Drug Administration (FDA) approval for Guardant360 CDx as a companion diagnostic to identify patients with hormone receptor (HR)-positive, HER2-negative advanced or metastatic breast cancer whose tumors develop ESR1 mutations before radiographic disease progression. The liquid biopsy can help identify patients who may benefit from ETCAMAH™ (camizestrant), AstraZeneca’s next-generation oral selective estrogen receptor degrader (SERD). This makes Guardant360 CDx the first FDA-approved liquid biopsy companion diagnostic for longitudinal testing in breast cancer.

The approval is based on findings from the pivotal SERENA-6 clinical trial, which evaluated whether circulating tumor DNA (ctDNA) testing could detect emerging ESR1 mutations before radiographic progression and support an earlier change in treatment. The approach differs from the traditional model of waiting for clinical or imaging evidence of progression before adapting therapy. Instead, patients were monitored for molecular signs of resistance while continuing their first-line endocrine treatment.

“This approval represents a landmark shift in how we define disease progression and reinforces the transformative role of liquid biopsy in guiding therapy decisions earlier at a critical moment in a breast cancer patient’s treatment journey,” said Helmy Eltoukhy, Guardant Health chairman and co-CEO.

“The SERENA-6 paradigm opens a new frontier in how cancer is managed, with potential application across different diseases and therapies.”

Using ctDNA to detect treatment resistance earlier

ESR1 mutations can emerge as breast cancer develops resistance to aromatase inhibitors, making their early detection relevant to treatment decisions. In SERENA-6, patients receiving an aromatase inhibitor with a cyclin-dependent kinase (CDK) 4/6 inhibitor underwent Guardant360 CDx testing every three months. When an eligible ESR1 mutation was detected before radiographic progression, patients switched to camizestrant while continuing their CDK4/6 inhibitor.

Patients managed using this ctDNA-guided strategy experienced a 56% reduction in the risk of disease progression or death compared with those who continued an aromatase inhibitor and CDK4/6 inhibitor after ESR1 mutation detection. Median progression-free survival was 16.0 months versus 9.2 months, representing 74% longer median progression-free survival. The study also found a 47% reduction in the risk of deterioration in global health status and quality of life.

These results support the potential clinical value of identifying molecular resistance before it becomes visible on imaging. By detecting an ESR1 mutation earlier, clinicians may have an opportunity to change treatment before conventional radiographic progression occurs. The strategy therefore places longitudinal molecular monitoring alongside imaging as a potential tool for managing advanced breast cancer.

FDA approval expands the role of liquid biopsy

The approval adds to the growing use of liquid biopsy in precision oncology, particularly for monitoring molecular changes during treatment. Unlike a single biomarker test performed at one point in a patient’s care, longitudinal ctDNA testing can provide repeated information about how a tumor is evolving and whether resistance-associated mutations are emerging.

Guardant Health estimates that approximately 37,000 women in the U.S. living with advanced HR-positive breast cancer and receiving an aromatase inhibitor could potentially benefit from this treatment approach. The company says the approval represents a shift toward using molecular signals to guide treatment decisions before radiographic progression. Further research will determine whether similar ctDNA-guided strategies can be applied across other cancers and therapies.

Guardant360 CDx expands companion diagnostic indications

Guardant360 CDx is an FDA-approved liquid biopsy platform for comprehensive genomic profiling across solid tumors. It detects multiple genomic alterations and has companion diagnostic indications covering cancers including breast cancer, non-small cell lung cancer and colorectal cancer. With the latest FDA approval, Guardant Health says the platform now has 29 companion diagnostic indications across multiple tumor types globally.

The approval follows a multi-year collaboration between Guardant Health and AstraZeneca. Guardant Health supported SERENA-6 using its FDA-approved Guardant360 CDx platform to detect ESR1 mutations across serial testing timepoints, providing the biomarker information needed to guide treatment changes. The company also reports that the test has coverage through Medicare and commercial payers representing more than 300 million covered lives.

The SERENA-6 findings highlight the potential of ctDNA testing to provide actionable information before conventional imaging detects disease progression. For HR-positive, HER2-negative advanced or metastatic breast cancer, the FDA approval gives Guardant360 CDx a specific role in longitudinal ESR1 mutation monitoring and treatment selection. It also adds to the broader evidence for integrating liquid biopsy into ongoing cancer management.

Source

Guardant Health

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