In a first for breast cancer, the Guardant360 CDx test has been FDA approved as a companion diagnostic for “serial” use with AstraZeneca’s ETCAMAH (camizestrant) in certain patients, Guardant Health has announced.
The test is for patients with hormone receptor (HR)-positive, HER2-negative advanced or metastatic breast cancer. It is used every three months during therapy to detect emerging ESR1 mutations before clinical or radiographic disease progression. Guardant360 CDx guided treatment with camizestrant plus a CDK4/6 inhibitor reduced the risk of disease progression or death by more than 50%.
This is the first FDA-approved liquid biopsy companion diagnostic for longitudinal, or serial, testing in breast cancer. As such, it represents a paradigm shift, the company says.
“For decades, doctors have largely waited for a scan to show that a tumor has grown before changing treatment,” Helmy Eltoukhy, Guardant Health chairman and co-CEO told Inside Precision Medicine. “Now, Guardant360, via a simple blood draw, can detect the molecular signs that a cancer is beginning to escape treatment, months before that progression may be visible on a scan, giving doctors an opportunity to switch therapy while the disease is still under control.”
That makes Guardant360 CDx the first FDA-approved liquid biopsy companion diagnostic for this type of “longitudinal” testing, or prognostic testing throughout treatment, in breast cancer management.
The test was first approved in 2020 and was the first NGS-based liquid biopsy. “This is important as guidelines recommend genomic testing only by comprehensive genomic profiling, which up until this point was inaccessible by liquid biopsy,” Eltoukhy said.
The test detects multiple genomic alterations across all solid tumors and was previously approved as a companion diagnostic in non-small cell lung cancer, breast cancer, and colorectal cancer treatment. It is approved as a companion diagnostic for ESR1 mutations to select patients for three other SERDs besides ETCAMAH.
Approximately 37,000 women in the U.S. live with advanced HR-positive breast cancer. ETCAMAH is a next-generation oral selective estrogen receptor degrader (SERD). This approval was based on data from the pivotal SERENA-6 clinical trial, which introduced a first-of-its-kind treatment strategy using ctDNA monitoring to detect emerging ESR1 resistance mutations before radiographic disease progression.
Patients enrolled in the study underwent serial testing with Guardant360 CDx every three months while receiving an aromatase inhibitor with a CDK4/6 inhibitor. Upon detection of an ESR1 mutation before radiographic progression, eligible patients were transitioned to camizestrant-based treatment. Patients treated this way experienced 74% longer median progression-free survival (16.0 vs. 9.2 months) with a 47% reduction in risk of deterioration in global health status and quality of life.
“This approval represents a landmark shift in how we define disease progression and reinforces the transformative role of liquid biopsy in guiding therapy decisions earlier at a critical moment in a breast cancer patient’s treatment journey,” Eltoukhy added. “The SERENA-6 paradigm opens a new frontier in how cancer is managed, with potential application across different diseases and therapies.”
The study came from a multi-year collaboration between Guardant Health and AstraZeneca focused on integrating Guardant Health products and capabilities into clinical development. It used Guardant’s FDA-approved Guardant360 CDx platform.
This latest FDA approval is the 29th CDx indication for Guardant360 CDx, globally. This “Builds on the platform’s increasing clinical use and broad coverage by Medicare and commercial payers, representing more than 300 million covered lives,” the company reports.
