Abstract PS3-08-27: Repower: a real-world noninterventional study of outcomes and experiences in patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2−) early breast cancer (EBC) treated with an adjuvant cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) plus endocrine therapy (ET)

Abstract Background: Ribociclib plus a nonsteroidal aromatase inhibitor demonstrated a significant invasive disease-free survival (iDFS) benefit in a broad population of patients with HR+/HER2− EBC, including those with node-negative disease in the phase 3 NATALEE trial. Abemaciclib plus ET also showed a significant iDFS benefit in patients with high-risk node-positive HR+/HER2− EBC in the phase 3 monarchE trial. However, evidence gaps persist related to real-world effectiveness, patient experiences, and safety with CDK4/6is in EBC. REPOWER, a retrospective clinical charts review and prospective patient-reported outcome (PRO) assessment, aims to characterize patients, clinical benefit, treatment experiences, and safety associated with adjuvant CDK4/6i treatment in the real-world EBC setting. Study design: REPOWER is a multicenter, international (13 countries in North American, Europe, and Asia), noninterventional, hybrid study assessing effectiveness; adherence, treatment satisfaction, and quality of life through PROs; and safety in patients with HR+/HER2− EBC treated with a CDK4/6i + ET. Data will be collected from patients aged ≥18 years with HR+/HER2− stage II or III EBC who have initiated adjuvant treatment with a CDK4/6i, in accordance with its approved local label, within 14 days prior to enrollment. Patients who have had a local or distant breast cancer recurrence before the CDK4/6i initiation date, or who enrolled in clinical trials ≤12 months prior to the initiation date, will be excluded. This study has a hybrid design, including a retrospective analysis of patient data from electronic health records and prospective data from PRO questionnaires and interviews. Two groups will be included, patients treated with ribociclib + ET as the primary cohort and patients treated with abemaciclib + ET as an exploratory cohort. The index date (time T 0) will be defined as the initiation of adjuvant ribociclib/abemaciclib. Patients will be followed up from T0 until death, lost to follow-up, end of the study period, or enrollment in a clinical trial, whichever occurs first. The expected enrollment period will be between 12-18 months, with planned patient follow-up for ≥36 months and a maximum follow-up of 54 months. This trial aims to enroll approximately 2650 patients in the ribociclib + ET cohort and 250 patients in the abemaciclib + ET cohort. The primary and secondary objectives will assess patients in the ribociclib + ET cohort. Primary outcomes include iDFS and distant disease-free survival (defined using Standardized Definitions for Efficacy End Points criteria). Select secondary objectives include baseline characteristics, PROs (adherence, health-related quality of life, treatment satisfaction, work productivity, patient self-reported treatment experiences), safety, and treatment patterns in the adjuvant and metastatic settings if distant recurrences occur. Subgroup analyses by nodal status, menopausal status, stage, and chemotherapy use will be performed. The exploratory objectives will assess patients in the abemaciclib + ET cohort. Objectives include baseline characteristics, PROs, and adverse events. Citation Format: M. Lustberg, S. Wang, A. Casas, Y. Zhu, N. Derakshan, G. Mason, M. Campone, M. De Laurentiis, M. Fernandez-Abad, J. Sirieix, M. Akdere, F. Ye, P. Dominguez Castro, A. Ring. Repower: a real-world noninterventional study of outcomes and experiences in patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2−) early breast cancer (EBC) treated with an adjuvant cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) plus endocrine therapy (ET) abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-08-27.