• Approval recommends repeat Guardant360 CDx testing every three months during therapy to detect emerging ESR1 mutations before clinical or radiographic disease progression
• In the Phase III SERENA-6 trial, ctDNA-guided treatment using Guardant360 CDx with camizestrant plus a CDK4/6 inhibitor following detection of an ESR1 mutation reduced the risk of disease progression or death by 56%

Guardant Health, Inc. (Nasdaq: GH), a leading precision oncology company, today announced that the U.S. Food and Drug Administration (FDA) has approved Guardant360^® CDx as a companion diagnostic (CDx) to identify patients with hormone receptor (HR)-positive, HER2-negative advanced or metastatic breast cancer harboring tumors with ESR1 mutations before radiographic progression who may benefit from treatment with ETCAMAH^™ (camizestrant), AstraZeneca’s next-generation oral selective estrogen receptor degrader (SERD). Guardant360 CDx is the first FDA-approved liquid biopsy CDx for longitudinal testing in breast cancer, and this approval represents a major shift from therapy selection and switching post-radiographic progression to adaptive cancer management and early interception using pre-radiographic progression circulating tumor DNA (ctDNA) testing.

The approval is based on data from the pivotal SERENA-6 clinical trial, which introduced a first-of-its-kind treatment strategy using ctDNA monitoring to detect emerging ESR1 resistance mutations before radiographic disease progression. Patients who switched to ETCAMAH in combination with continuing a cyclin-dependent kinase (CDK) 4/6 inhibitor versus continuing treatment with an aromatase inhibitor with a CDK4/6 inhibitor following ESR1 mutation detection experienced a 56% reduction in the risk of progression or death. The trial demonstrated the clinical value of proactively identifying disease progression earlier than radiographic imaging and adapting therapy earlier in the course of disease.

“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.”

Approximately 37,000 women in the U.S. living with advanced HR-positive breast cancer being treated with an aromatase inhibitor could potentially benefit from this new therapeutic approach leading to better progression-free survival and outcomes.

Advancing a New Precision Medicine Paradigm

Historically, biomarker testing in advanced cancer most often occurred after clinical or radiographic progression. The SERENA-6 study demonstrated the value in a fundamentally different approach: ctDNA surveillance during first-line endocrine therapy to identify the emergence of resistance before overt disease progression.

Patients enrolled in the study underwent serial testing with Guardant360 CDx every three months while receiving an aromatase inhibitor with a CDK4/6 inhibitor. Upon detection of an ESR1 mutation before radiographic progression, eligible patients were transitioned to camizestrant-based treatment. Patients treated under this new paradigm experienced 74% longer median progression-free survival (16.0 vs. 9.2 months) with a 47% reduction in risk of deterioration in global health status and quality of life.

Strategic Collaboration with AstraZeneca

The approval reflects a multi-year collaboration between Guardant Health and AstraZeneca focused on integrating Guardant Health products and capabilities into clinical development.

Guardant Health supported the study through its FDA-approved Guardant360 CDx platform, providing high-sensitivity ESR1 mutation detection capabilities across serial testing timepoints. The collaboration enabled accessible, scalable biomarker testing designed to support rapid clinical decision-making and broad patient access.

This latest FDA approval for Guardant360 CDx marks the 29^th CDx indication across multiple tumor types globally, building on the platform’s increasing clinical utility and broad coverage by Medicare and commercial payers, representing more than 300 million covered lives.

About Guardant360® CDx

Guardant360 CDx is the first FDA-approved liquid biopsy for comprehensive genomic profiling. It detects multiple genomic alterations across all solid tumors and is approved as a companion diagnostic for therapies in non-small cell lung cancer, breast cancer, and colorectal cancer.

About Guardant Health

Guardant Health is a leading precision oncology company focused on guarding wellness and giving every person more time free from cancer. Founded in 2012, Guardant is transforming patient care and accelerating new cancer therapies by providing critical insights into what drives disease through its advanced blood and tissue tests, real-world data and AI analytics. Guardant tests help improve outcomes across all stages of care, including screening to find cancer early, monitoring for recurrence in early-stage cancer, and treatment selection for patients with advanced cancer. For more information, visit guardanthealth.com and follow the company on LinkedIn, X (Twitter) and Facebook.

Guardant Health Forward-Looking Statements

This press release contains forward-looking statements within the meaning of federal securities laws, including statements regarding the potential utilities, values, benefits and advantages of Guardant Health’s liquid biopsy tests or assays, which involve risks and uncertainties that could cause the actual results to differ materially from the anticipated results and expectations expressed in these forward-looking statements. These statements are based on current expectations, forecasts and assumptions, and actual outcomes and results could differ materially from these statements due to a number of factors. These and additional risks and uncertainties that could affect Guardant Health’s financial and operating results and cause actual results to differ materially from those indicated by the forward-looking statements made in this press release include those discussed under the captions “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operation” and elsewhere in its Annual Report on Form 10-K for the year ended December 31, 2025 and in its other reports filed with or furnished to the Securities and Exchange Commission. The forward-looking statements in this press release are based on information available to Guardant Health as of the date hereof, and Guardant Health disclaims any obligation to update any forward-looking statements provided to reflect any change in its expectations or any change in events, conditions, or circumstances on which any such statement is based, except as required by law. These forward-looking statements should not be relied upon as representing Guardant Health’s views as of any date subsequent to the date of this press release.

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