Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors haveshown promising survival outcomes with additional treatments to the traditionalendocrine therapy (ET) in patients with hormone receptor-positive (HR-positive)and human epidermal growth factor receptor type 2 negative (HER2–negative)advanced breast cancer (aBC). The gene discussed is ERBB2; the disease is aneurysmal bone cyst.