Palo Alto, California — September 4, 2026
Guardant Health announced that the U.S. Food and Drug Administration (FDA) has approved Guardant360® CDx as a companion diagnostic (CDx) for AstraZeneca’s ETCAMAH™ (camizestrant) in patients with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer whose tumors develop ESR1 mutations before radiographic disease progression. The approval represents a major regulatory milestone for Guardant Health and expands the role of its liquid-biopsy platform in precision oncology and treatment monitoring. Importantly, the FDA approval recommends repeat Guardant360 CDx testing every three months during therapy, enabling clinicians to monitor circulating tumor DNA (ctDNA) for emerging ESR1 mutations before conventional imaging identifies disease progression. Guardant Health said this makes Guardant360 CDx the first FDA-approved liquid-biopsy companion diagnostic for longitudinal testing in breast cancer. The regulatory decision moves the use of liquid biopsy beyond a single treatment-selection test toward repeated molecular monitoring that can support earlier treatment decisions during a patient’s treatment journey.
Guardant360 CDx Enables Serial ESR1 Mutation Monitoring
The FDA approval is based on findings from the Phase III SERENA-6 clinical trial, which evaluated a ctDNA-guided treatment strategy using serial biomarker testing. Patients receiving an aromatase inhibitor together with a CDK4/6 inhibitor underwent Guardant360 CDx testing every three months to identify emerging ESR1 resistance mutations. Patients who developed an eligible ESR1 mutation before radiographic progression could transition to camizestrant-based therapy while continuing a CDK4/6 inhibitor. This approach represents a shift in how molecular progression can be monitored during cancer treatment, with Guardant360 CDx serving as the testing platform for identifying resistance-associated changes in tumor DNA circulating in the bloodstream. The regulatory milestone strengthens Guardant Health’s position in the liquid-biopsy companion diagnostic market, particularly as pharmaceutical developers increasingly incorporate molecular monitoring into treatment strategies. By enabling repeated testing during therapy, the platform provides a framework for identifying clinically relevant genomic changes before conventional radiographic assessment.
SERENA-6 Data Support ctDNA-Guided Treatment Strategy
In the pivotal SERENA-6 trial, patients whose treatment was adapted after detection of an emerging ESR1 mutation experienced a 56% reduction in the risk of disease progression or death compared with patients who continued an aromatase inhibitor plus a CDK4/6 inhibitor. Median progression-free survival was 16.0 months versus 9.2 months, representing a 74% longer median progression-free survival for the ctDNA-guided treatment strategy. The study also reported a reduction in the risk of deterioration in global health status and quality of life. These findings provided the clinical foundation for the FDA’s companion-diagnostic approval and demonstrate how serial molecular testing can be integrated into treatment decisions. For Guardant Health, the outcome further validates the use of ctDNA-based monitoring as an actionable component of precision oncology. The company said approximately 37,000 women in the United States receiving aromatase inhibitor therapy for advanced HR-positive breast cancer could potentially benefit from the new treatment approach.
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Guardant Health Expands Precision Oncology CDx Platform
The approval also strengthens a long-term collaboration between Guardant Health and AstraZeneca focused on integrating Guardant’s diagnostic technologies into clinical development and precision-medicine strategies. Guardant Health supported SERENA-6 through its FDA-approved Guardant360 CDx platform, providing high-sensitivity detection of ESR1 mutations across serial testing timepoints. The latest decision represents the platform’s 29th companion-diagnostic indication globally across multiple tumor types, according to the company. Guardant360 CDx already provides genomic profiling across solid tumors and has companion-diagnostic applications spanning breast, colorectal and non-small cell lung cancers. The new breast-cancer indication further expands the platform’s clinical utility from genomic profiling and treatment selection toward longitudinal disease monitoring. The FDA decision therefore marks an important regulatory and commercial milestone for Guardant Health, reinforcing the company’s strategy of using blood-based genomic testing to support treatment decisions throughout the cancer-care pathway.
Source: Guardant Health, press relese
