MonarcHER, a phase II trial in women with HR-positive/HER2-positive ABC who had previously received at least two HER2-targeted therapies for ABC, reported that a three-drug combination of abemaciclib, trastuzumab, and fulvestrant significantly prolonged PFS compared to standard-of-care chemotherapy plus trastuzumab [17]. Here, ERBB2 is linked to aneurysmal bone cyst.