Palbociclib and Fulvestrant Combined Regimen Induced Prolonged Bone Metastasis Control of Stage IV HR+/HER2- Breast Cancer: A Case Report.

The management of advanced metastasized breast cancer (BC) is a clinically challenging entity with a wide spectrum of novel therapeutics being introduced to the market. Such agents have remodeled BC treatment landscape and prolonged patients' survival. Over the past decade, a growing body of literature has shed lights on CDK4/6 involvement in oncogenesis and the role of its inhibitors in clinical use with palbociclib being the prototype drug. We present a case of a 58-year-old post-menopausal Middle-Eastern woman diagnosed with stage IV HR+/HER2- breast cancer with extensive bone metastasis. The lesions were widely distributed across the axial skeleton including base of the skull, sternum, ribs, left iliac bone, right inferior pubic ramus, cervical, thoracic, and lumbosacral vertebrae. The patient was started on therapeutic doses of letrozole and zoledronic acid in conjunction with adjuvant radiotherapy. A significant partial response was achieved reaching 70% remission followed by sternum disease progression. A decision was made to switch letrozole for tamoxifen which resulted in disease stability. Due to postmenopausal bleeding, tamoxifen was held and letrozole was reintroduced leading to regimen failure and disease advancement. Palbociclib and fulvestrant were started accordingly, yielding a remarkable metabolic response of all bone metastatic lesions (stable disease) after three months of the regimen initiation. The aforementioned stable disease status continued for approximately three years up to this point.