Guardant360 CDx Receives Companion Diagnostic Designation in ESR1+ Breast Cancer

Guardant 360 CDx has been approved by the FDA as a companion diagnostic for patients with ESR1-mutant, estrogen receptor (ER)–positive, HER2-negative advanced or metastatic breast cancer who may be eligible for treatment with elacestrant (Orserdu), according to a press release from Guardant Health.¹

The FDA approval for Guardant 360 CDx "is great news for [patients with] breast cancer [and] ESR1 mutations who now have, for the first time, an approved treatment for their specific type of cancer and a blood-based companion diagnostic," according to an expert from Guardant Health.

The approval for the liquid biopsy assay follows the FDA approval of elacestrant as a treatment for patients with ESR1-positive, ER-positive, HER2-negative advanced or metastatic breast cancer who had progressed on a minimum of 1 line of endocrine therapy.² The agent was approved under FDA priority review designation.

“This FDA approval is great news for [patients with] breast cancer [and] ESR1 mutations who now have, for the first time, an approved treatment for their specific type of cancer and a blood-based companion diagnostic,” Helmy Eltoukhy, co-chief executive officer at Guardant Health, said in the press release. “We are pleased that the Guardant360 CDx liquid biopsy is now approved so that oncologists and their patients can access comprehensive genomic profiling to see if they are eligible to receive this therapy.”

Using a blood draw, it is possible to examine all genes recommended by the National Comprehensive Cancer Network in 7 days that are suggested for clinical care and by non–small cell lung (NSCLC) cancer treatment guidelines. Although the diagnostic tool has been approved for several NSCLC indications, this marks its first approval for patients diagnosed with breast cancer.

Elacestrant was approved based on findings from the phase 3 EMERALD trial (NCT03778931), in which patients achieved a median progression-free survival of 3.8 months (95% CI, 2.2-7.3) following treatment with the agent compared with 1.9 months (95% CI, 1.9-2.1) among those treated with fulvestrant or other aromatase inhibitors (HR, 0.55; 95% CI, 0.39-0.77; 2-sided P = .0005).

This translated to a 45% reduction in risk of death or progression in the population vs standard of care. Moreover, the FDA identified 345 mg as the recommended dose of the oral agent.

In terms of safety, the most frequent adverse effects were grade 1/2 nausea and musculoskeletal pain. Investigators did not report any events of hematologic toxicities and no patients in either arm developed sinus bradycardia.

References

1. Guardant Health receives FDA approval for Guardant360® CDx as companion diagnostic for Menarini Group’s ORSERDU™ for treatment of patients with ESR1 mutations in ER+, HER2- advanced or metastatic breast cancer. News release. Guardant Health. January 30, 2023. Accessed January 31, 2023. http://bit.ly/3DobE1h
2. FDA approves elacestrant for ER-positive, HER2-negative, ESR1-mutated advanced or metastatic breast cancer. News release. FDA. January 27, 2023. Accessed January 27, 2023. bit.ly/3kQrxHq