You may have heard that the U.S. Food and Drug Administration (FDA) approved elacestrant for postmenopausal women or adult men with estrogen receptor (ER)-positive, HER2-negative, ESR1-mutated advanced or metastatic breast cancer on January 27, 2023. In addition, the FDA also approved the Guardant360 CDx assay, a companion liquid biopsy diagnostic device for identifying patients for treatment.