[A Case of a Patient with Hormone-Positive HER2-Negative Breast Cancer Whose Multiple Brain Metastases Disappeared after Abemaciclib Combination Therapy].

The patient was a 38-year-old premenopausal woman. Under the diagnosis of left breast cancer with cT2N3cM1(OSS), Stage Ⅳ, Luminal B like, we started treatment with anastrozole, leuprorelin, abemaciclib and denosumab. Two months after starting treatment, headache and nausea were observed. A contrast-enhanced MR scan of the head showed 2 brain metastases measuring 3 mm in the right frontal lobe and 7 mm in the left frontal cortex. Radiotherapy and surgical resection were considered for the brain metastases. However, due to the possibility of neurological complications and the short time since abemaciclib was administered, the patient was continued on the same treatment until the efficacy of the treatment was determined. Three months after restarting treatment, an MRI of the head showed that the brain metastases had disappeared. The primary tumor had shrunk and some of the lymph nodes were obscured. Fifteen months has passed since the brain metastases disappeared, but no new lesions have been observed and the patient continues to receive abemaciclib therapy. Abemaciclib has been shown to cross the blood-brain barrier. It also has a longer intracerebral retention time than other CDK4/6 inhibitors. Combination therapy with abemaciclib may be a useful treatment option for HR-positive, HER2-negative breast cancer with brain metastases.