ESR1 and aneurysmal bone cyst: We evaluated 301 HER2− ABC patients treated at 3 institutions with 172 patients (119 estrogen receptor-positive [ER+], 47 ER−, 6 unknown) receiving eribulin (eribulin group) and 129 patients (92 ER+, 31 ER−, 6 unknown) not receiving eribulin (non-eribulin group).