SRS & Abemaciclib w/wo Imlunestrant in the Management of HR+/HER2- Breast CA Brain Metastases

The study is designed as a prospective, single-arm, nonrandomized, open-label, phase I/II trial of abemaciclib and endocrine therapy with stereotactic radiosurgery (SRS) among patients with hormone receptor (HR)+/HER2- metastatic breast cancer brain metastases. Treatment will be initiated with one week of abemaciclib followed by stereotactic radiation to sites of brain metastases or post-operative cavities with continued abemaciclib. Safety will be monitored initially by a 3+3 design. This will be followed by a phase 2 study to evaluate intracranial progression free survival (PFS). If unexpected neurologic toxicities are noted, the dose of radiation therapy will be modified.