Precision oncology company Guardant Health Inc (Nasdaq:GH) announced on Friday that the US Food and Drug Administration (FDA) has approved Guardant360 CDx as a companion diagnostic for AstraZeneca's ETCAMAH (camizestrant) in patients with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer with ESR1 mutations before radiographic progression.

The approval recommends repeat Guardant360 CDx testing every three months during therapy to identify emerging ESR1 mutations and support earlier treatment adaptation.

Guardant360 CDx is the first FDA-approved liquid biopsy CDx for longitudinal testing in breast cancer, and this approval and shifts biomarker monitoring toward detecting resistance before radiographic progression.

The decision is based on the Phase III SERENA-6 trial, in which patients who switched to camizestrant plus a CDK4/6 inhibitor after ESR1 mutation detection experienced a 56% reduction in the risk of disease progression or death versus continuing an aromatase inhibitor with a CDK4/6 inhibitor.

The ctDNA-guided approach produced a median progression-free survival of 16.0 months versus 9.2 months, while reducing the risk of deterioration in global health status and quality of life by 47%.

Guardant Health said approximately 37,000 women in the United States with advanced hormone receptor-positive breast cancer treated with an aromatase inhibitor could potentially benefit from the approach.

The approval is Guardant360 CDx's 29th companion diagnostic indication across multiple tumour types globally and follows a multi-year collaboration with AstraZeneca to support biomarker testing and clinical development.