CDK4 and breast carcinoma: Additionally, a retrospective single-institution analysis suggested that 15 out a cohort of 42 pts with ESR1+ breast cancer with brain metastases showed promising results using CDK4 and CDK6 inhibitors palbociclib or abemaciclib for 6 months combined with stereotactic radiation [71] and only 5% of the patients developed radiation necrosis.