Long-Term Control of Breast Cancer Brain Metastases Using Abemaciclib and Letrozole Combination Therapy: A Case Report.

Breast cancer brain metastases are among the most common distant metastases and have a poor prognosis. However, the effects of subtype-specific systemic therapy on breast cancer brain metastases are unknown. This report highlights the long-term control of breast cancer brain metastases using abemaciclib and letrozole combination therapy without severe side effects. We report a case of a middle-aged premenopausal female patient who experienced convulsions and was diagnosed with hormone receptor-positive breast cancer brain metastases. After standard-of-care whole-brain radiation therapy, systemic chemotherapy was administered, and the primary tumor and multiple brain metastases were sufficiently reduced. However, treatment was discontinued because peripheral neuropathy worsened. Abemaciclib, letrozole, and luteinizing hormone-releasing hormone agonists were administered as maintenance therapy. The treatment maintained a stable disease and no new lesions were observed. Cyclin-dependent kinase 4/6 inhibitors and endocrine maintenance therapy are effective treatments for breast cancer brain metastases.