Background Abemaciclib is a selective CDK4 & 6 inhibitor approved to treat patients (pts) with HR+, HER2- advanced breast cancer (ABC) on a continuous dosing schedule as monotherapy or in combination with endocrine therapy.1,2,3 Clinical data demonstrate that abemaciclib can penetrate the blood brain barrier resulting in comparable abemaciclib concentrations in brain metastases tissues, cerebrospinal fluid, and plasma.4 We report safety and efficacy results of abemaciclib in pts with leptomening...