Study of Abemaciclib and Elacestrant in Participants With Brain Metastasis Due to ER+/HER-2- Breast Cancer

Required: ESR1 overexpression (≥ 1% staining by IHC)

Documentation of ER positive tumor with ≥ 1% staining by immunohistochemistry (IHC) as defined in the 2010 or 2020 American Society for Clinical Oncology (ASCO) recommendations for ER testing

Required: HER2 (ERBB2) negative (IHC 0 or 1+ or ISH negative)

HER-2 negative tumor with an IHC result of 0 or 1+ for cellular membrane protein expression or an in situ hybridization negative result as defined in the 2013 or 2018 ASCO recommendations for HER-2 testing

Must have received: endocrine therapy — metastatic

At least one endocrine therapy

Cannot have received: CDK4/6 inhibitor (abemaciclib)

Exception: Use of abemaciclib in the adjuvant setting is allowed if the last treatment administration was more than 12 months prior to first recurrence.

Prior therapy with abemaciclib in the metastatic setting. Note: Use of abemaciclib in the adjuvant setting is allowed if the last treatment administration was more than 12 months prior to first recurrence.

Cannot have received: selective estrogen receptor degrader (elacestrant)

Prior therapy with elacestrant or other investigational selective estrogen receptor degraders (SERDs), or investigational alike agents such as selective estrogen receptor modulators (SERMs), selective estrogen receptor covalent antagonists (SERCANs), complete estrogen receptor antagonists (CERANs), and proteolysistargeting chimeras (PROTACs) in the metastatic setting.