A Probable Case of Cerebral Amyloid Angiopathy-Related Inflammation Temporally Associated with Abemaciclib: A Case Report.

Introduction: Abemaciclib, a cyclin-dependent kinase 4/6 inhibitor that has the ability to penetrate breast tissue and the blood-brain barrier, has been used as an addition to endocrine therapy in breast cancer. Adverse effects like infections, nausea and vomiting, diarrhoea, fatigue, cytopenia (including neutropenia) have been mentioned quite frequently. Case Presentation: Here, we present the first report of a possible temporal association in a patient who has been treated with abemaciclib due to an unresectable breast carcinoma and developed cerebral amyloid angiopathy-related inflammation (CAA-ri). Two months after start of treatment with abemaciclib, progressive cognitive impairment was seen (with dyscalculia, behavioural changes, apraxia, and eventually bradyphrenia). Although abemaciclib dosage was reduced and eventually discontinued, the patient experienced three tonic-clonic seizures a week later and was unresponsive afterwards. A CT scan and a subsequent MRI scan showed the imaging characteristics of probable CAA-ri. Furthermore, alternative diagnoses were excluded, and after immunosuppressive therapy, clinical and radiological improvement occurred. Conclusion: Considering this clinical course, a temporal association with abemaciclib has been proposed.