Abstract CT074: ELECTRA: An open-label, multicenter, phase 1b/2 study of elacestrant in combination with abemaciclib in patients with brain metastasis from estrogen receptor-positive (ER+), HER2-negative (HER2-) breast cancer (BC)

Abstract

Abstract Background: Endocrine therapy (ET) + cyclin dependent kinase 4/6 inhibitor (CDK4/6i) is the mainstay for the management of ER+/HER2- mBC as 1st-line therapy. However, tumors eventually develop resistance to ET, leading to disease progression. In the EMERALD phase 3 trial, single-agent elacestrant was associated with significantly prolonged progression-free survival (PFS) and a manageable safety profile vs standard of care (SOC) ET, leading to the first oral SERD approval. Patients receiving elacestrant experienced a median PFS (mPFS) of 3.8 months vs 1.9 months with SOC (Bidard, 2022). Patients who received ≥12 months of prior CDK4/6i experienced a mPFS of 8.6 months with elacestrant vs 1.9 months with SOC (SABCS, 2022). Currently, there are no approved systemic treatments for patients with ER+/HER2- BC who have brain metastasis. The rationale for the ELECTRA study is to combine elacestrant with abemaciclib in patients with brain metastasis, given both compounds have demonstrated the ability to cross the blood-brain barrier (Conlan, 2020; Tolaney, 2020). Methods: ELECTRA (NCT05386108) is an open-label phase 1b/2, multicenter study evaluating elacestrant in combination with abemaciclib. Eligibility includes patients with ER+/HER2- locally advanced or metastatic BC and measurable brain metastasis. For phase 1b, the presence of brain metastasis is not required for eligibility. For phase 2, patients must have ≥ 1 active and measurable brain metastasis per RECIST v1.1. Patients must have received prior therapy in the metastatic setting, including ≥ 1 endocrine therapy, ≤ 2 chemotherapy regimens, and 0-2 prior CDK4/6i (excluding abemaciclib). The phase 1b primary objective is to determine the recommended phase 2 dose (RP2D); secondary objectives include safety, pharmacokinetics (PK), overall response rate (ORR), duration of response (DoR), clinical benefit rate (CBR), PFS, and overall survival (OS). The phase 2 primary objective is ORR per RECIST v1.1; secondary objectives include intracranial response rate, DoR, CBR, PFS, OS, PK, and quality of life. The phase 1b portion of the trial is actively ongoing to determine the RP2D with study sites open worldwide. Citation Format: Erika Hamilton, Sung-Bae Kim, Nancy U. Lin, Ahmad Awada, Eva Ciruelos Gil, Alessandro Di Sanzo, Bartomeu Piza Vallespir, Kathy Puyana Theall, Nuhad Ibrahim. ELECTRA: An open-label, multicenter, phase 1b/2 study of elacestrant in combination with abemaciclib in patients with brain metastasis from estrogen receptor-positive (ER+), HER2-negative (HER2-) breast cancer (BC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT074.