In the clinical setting, elacestrant 400 mg daily has demonstrated an objective response rate (ORR) of 19.4% and median PFS of 4.5 months in a phase 1 trial (RAD1901-005) of heavily pretreated postmenopausal women with ER+/human epidermal growth factor receptor (HER)2− advanced/metastatic breast cancer (ABC/mBC) [18]. The gene discussed is ERBB2; the disease is aneurysmal bone cyst.