• Study results suggest Guardant Reveal^TM circulating tumor DNA blood test may help clinicians decide to pursue more or less aggressive post-surgical chemotherapy regimens
• PEGASUS is first clinical utility trial for tissue-free detection of minimal residual disease

Guardant Health, Inc. (Nasdaq: GH), a leading precision oncology company, today announced that initial results from the PEGASUS trial suggest liquid biopsy may be used in post-surgical clinical management to reduce unnecessary toxicity from chemotherapy and improve the response to standard chemotherapy regimens in patients with stage III or high-risk stage II colon cancer. Results from the trial, which is an ISS study sponsored by IFOM ETS – the AIRC Institute of Molecular Oncology in Milan, Italy, and supported by Guardant Health, were presented today by study investigators at the ESMO Congress in Madrid, Spain.

One of the first prospective studies using liquid biopsy, the PEGASUS trial includes 135 patients recruited from 11 cancer centers in Italy and Spain. The study is assessing the feasibility of escalating or de-escalating adjuvant (post-surgery) chemotherapy based on the presence or absence of minimal residual disease (MRD) as indicated by circulating tumor DNA (ctDNA) detected by the Guardant Reveal blood test at multiple timepoints. Patients with positive results receive standard chemotherapy, while patients with negative results receive a milder therapy that is associated with significantly less acute and chronic neurological toxicity compared to standard treatment. Liquid biopsy is repeated several times along the course of treatment to reveal opportunities to treat patients safely with lower toxicity regimens, identify therapeutic resistance, and tailor chemotherapy to be stronger when needed.

Initial results show that 34% of patients with a positive liquid biopsy result after surgery had the cancer return, while only 10% of patients with a negative result experienced a relapse. Approximately 40% of patients converted from ctDNA-positive to ctDNA-negative after treatment, suggesting treatment efficacy of chemotherapy for some patients.

“We are confident that, once confirmed by the results of several other ongoing international studies on liquid biopsy, our findings may help influence the modification of clinical practice guidelines for the treatment of operable colon cancer, supporting adjuvant therapy scale-down or elimination in patients with negative liquid biopsy, and chemotherapy personalization in the case of molecular non-response,” said Silvia Marsoni, MD, PhD, the designer of the PEGASUS trial and head of the precision oncology unit at IFOM. “A shift from the current paradigm of one-size-fits-all chemotherapy toward a new paradigm of tailored therapies is not the only expected impact of the PEGASUS trial. It will allow us to explore the biology of micro-metastatic tumors, for which we need to find new and more effective therapies.”

“Currently a significant number of patients with stage II and III colon cancer do not receive the intended benefit from adjuvant chemotherapy due to limits of current prognostic criteria. There is a significant need for better prognostic tools to guide clinical management in this patient population,” said Craig Eagle, MD, Guardant Health chief medical officer. “These initial trial results are promising and suggest that the Guardant Reveal liquid biopsy test can provide a sensitive tool to detect MRD and predict recurrence of the cancer, helping oncologists make informed treatment decisions that improve outcomes for their patients.”

For more information about the PEGASUS study, visit: https://guardanthealth.com/clinical-studies/#early-stage-studies--content

About Guardant Health

Guardant Health is a leading precision oncology company focused on helping conquer cancer globally through use of its proprietary tests, vast data sets and advanced analytics. The Guardant Health oncology platform leverages capabilities to drive commercial adoption, improve patient clinical outcomes and lower healthcare costs across all stages of the cancer care continuum. Guardant Health has commercially launched Guardant360®, Guardant360 CDx, Guardant360 TissueNext™, Guardant360 Response™, and GuardantINFINITY® tests for advanced stage cancer, and Guardant Reveal™ for early-stage cancer. The Guardant Health screening portfolio, including the commercially launched Shield™ test, aims to address the needs of individuals eligible for cancer screening. For more information, visit guardanthealth.com and follow the company on LinkedIn and Twitter.

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, 2022, and any current and periodic reports filed with or furnished to the Securities and Exchange Commission thereafter. 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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