Guardant360® CDx is the first companion diagnostic to be approved in Japan to identify ESR1 mutations in patients with hormone receptor-positive, HER2-negative breast cancer for treatment with imlunestrant

TOKYO, Dec. 22, 2025 /PRNewswire/ -- Guardant Health Japan Corp. today announced that the Ministry of Health, Labour and Welfare (MHLW) has approved Guardant360® CDx on 23 October 2025 as a companion diagnostic to identify ESR1 mutations in patients with hormone receptor–positive, HER2-negative breast cancer with disease progression following endocrine therapy, for consideration of treatment with imlunestrant. This approval makes Guardant360® CDx comprehensive genomic profiling panel the first blood-based companion diagnostic to be approved in Japan for the detection of ESR1 mutations.

The ESR1 gene encodes the estrogen receptor alpha proteins, one of the key hormone receptors involved in breast cancer. ESR1 mutations are recognized drivers of resistance to aromatase inhibitors, a class of endocrine therapies widely used as first-line treatment in breast cancer. In a randomized multicenter trial, ESR1 mutations were detected approximately 20 to 40% of patients with locally advanced or metastatic breast cancer previously treated with an aromatase inhibitor¹, and it has been reported ESR1 mutation prevalence increased with additional lines of therapy².

This regulatory approval of the Guardant360® CDx test, which identifies ESR1 mutations using a blood sample, is expected to increase targeted treatment options for patients with hormone receptor–positive, HER2-negative breast cancer who have developed resistance to aromatase inhibitors.

Guardant360® CDx was approved by MHLW in March 2022 for comprehensive genomic profiling in patients with advanced solid tumors. The test is approved as a companion diagnostic for multiple cancer drugs approved in Japan. Testing under the national health insurance system is available at cancer genome core hospitals, cancer genome hub hospitals, and affiliated cancer genome medical institutions designated by MHLW. Please refer to Annex A for the list of approved companion diagnostics.

References:

1. Jhaveri KL, et al. N Engl J Med. 2025; 392(12): 1189-1202. 
2. Bhave MA, et al. Breast Cancer Res Treat. 2024; 207: 599-609. 

About Guardant360^® CDx 

Guardant360^® CDx is a liquid biopsy test that uses next generation sequencing to analyse circulating tumour DNA (ctDNA), which is produced when tumours shed small pieces of their genetic material into the bloodstream. The test provides comprehensive genomic profiling results from a simple blood draw, helping oncologists move beyond the limitations of tissue biopsies to obtain clinically relevant information in time to match patients to the optimal personalized treatment.

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, please visit https://guardanthealthjapan.com and follow the company on LinkedIn.

* The complete portfolio of Guardant Health products may not be available in all regions. 

Forward-Looking Statements

This news 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, 2024 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.

Annex A

Note: Underlined item has been added with this approval.