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

Guardant Health Japan Corp.  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 therapy.

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.