As reported on Fierce BioTech, Guardant Health has secured U.S. Food and Drug Administration approval for its Guardant360 CDx liquid biopsy test as the companion diagnostic for AstraZeneca’s newly approved breast cancer therapy, Etcamah.
The authorization follows the FDA’s Sept. 4 approval of Etcamah for use alongside a CDK4/6 inhibitor in patients with hormone receptor-positive, HER2-negative, locally advanced or metastatic breast cancer whose tumors develop an ESR1 mutation during treatment with an aromatase inhibitor and a CDK4/6 inhibitor.
According to AstraZeneca, identification of the ESR1 mutation must be performed using an FDA-authorized diagnostic assay. Guardant360 CDx received approval for that role on the same day as the drug, enabling clinicians to monitor patients throughout treatment. The companies recommend repeat testing every three months to detect newly emerging ESR1 mutations before evidence of disease progression appears on imaging studies or through clinical assessment.
Guardant Health said the approval introduces a new strategy for biomarker-guided cancer care. Traditionally, therapy changes in advanced cancer have generally occurred after radiographic or clinical progression is observed. In contrast, serial liquid biopsy monitoring may allow physicians to identify molecular signs of treatment resistance earlier and adjust therapy before tumors visibly worsen.
The approach was evaluated in the Phase 3 SERENA-6 trial, where patients receiving first-line treatment with an aromatase inhibitor plus a CDK4/6 inhibitor underwent Guardant360 CDx testing at three-month intervals. Patients found to have developed ESR1 mutations before radiographic progression were eligible to transition to a camizestrant-based regimen.
Data from the study showed meaningful clinical benefits for patients managed under this monitoring strategy. Those who switched treatment following molecular detection of ESR1 mutations achieved a median progression-free survival of 16 months, compared with 9.2 months for patients who did not follow the approach. The strategy also reduced the risk of deterioration in overall health status and quality of life by 47%.
Guardant Health leadership characterized the approval as a significant advancement for precision oncology and liquid biopsy technology. Helmy Eltoukhy, the company’s chairman and co-chief executive officer, said the decision supports a new understanding of disease progression by enabling treatment decisions to be guided by molecular changes detected in blood samples before conventional signs of progression emerge.
As liquid biopsy continues to gain traction in oncology, the approval positions Guardant360 CDx as a tool for earlier identification of treatment resistance and more proactive management of advanced breast cancer.
