Endocrine therapy in combination with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors is currently the standard first-line treatment for patients with HR+/HER2− advanced breast cancer (ABC) (China Anti-cancer Association Committee of Breast Cancer Society, 2025; National Quality Control Center for Cancer Breast Cancer Expert Committee, 2023). Here, CDK4 is linked to aneurysmal bone cyst.