The U.S. Food and Drug Administration (FDA) has approved Guardant Health’s Guardant360 CDx liquid biopsy test as a companion diagnostic to identify advanced or metastatic breast cancer patients with ESR1 mutations who may benefit from treatment with ORSERDU (elacestrant).

ORSERDU is a nonsteroidal selective estrogen receptor degrader to be commercialized by Stemline Therapeutics, Inc., a subsidiary of Menarini Group.

Breast Cancer Diagnostics

Breast cancer is the second leading cause of cancer death in women. The American Cancer Society estimates that about 297,790 new cases of invasive breast cancer will be diagnosed in women in 2023, and about 43,700 women will die from breast cancer.1 ORSERDU is a therapy approved by the FDA for advanced breast cancer patients with ESR1 mutations, with disease progression following at least one line of endocrine therapy. ESR1 mutations are present in approximately 40% of ER+/HER2- advanced breast cancers.

“This FDA approval is great news for breast cancer patients with ESR1 mutations, who now have, for the first time, an approved treatment for their specific type of cancer and a blood-based companion diagnostic,” says Helmy Eltoukhy, Guardant Health co-CEO. “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.”

Guardant360 CDx as a Companion Diagnostic

The FDA approved Guardant360 CDx as a companion diagnostic (CDx) in conjunction with the approval of ORSERDU for postmenopausal women or adult men with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, ESR1-mutated, advanced or metastatic breast cancer with disease progression following at least one line of endocrine therapy.

“We are proud to bring the very first treatment targeting ESR1 mutations which are present in up to 40% of ER+/HER2- advanced breast cancers,” says Elcin Barker Ergun, CEO of Menarini Group. “We’re also pleased with the approval of the Guardant360 CDx blood test as the companion diagnostic to help oncologists identify patients who may benefit from this innovative endocrine therapy.”

The approval as a companion diagnostic for ORSERDU is Guardant Health’s fifth FDA approval for the Guardant360 CDx test and its first in breast cancer.


  1. Accessed January 11, 2023.