Abstract PD5-10: Pooled analysis of patients (pts) treated with 1st-line (1L) ribociclib (RIB) + endocrine therapy (ET) in the MONALEESA (ML) studies: long-term progression-free survival (PFS)

Abstract Background: RIB demonstrated clinically and statistically significant PFS and overall survival (OS) benefit in all of its phase 3 trials in HR+/HER2− advanced breast cancer (ABC; ML-2, -3, -7). We studied clinical characteristics and biomarkers of pts who derived long-term treatment benefit. We present an exploratory analysis of the ML trials of all 1L pts with long-term response (LTR; PFS >4 y) to RIB and 1L postmenopausal pts with very long-term response (VLTR; PFS >5 y). Methods: In the ML trials, pre- (ML-7) and postmenopausal (ML-2, -3) pts with HR+/HER2− ABC received RIB + ET or placebo + ET. Only pts who received 1L RIB were included in this pooled analysis. Pts with early relapse (treatment-free interval [TFI] ≤12 months on [neo]adjuvant ET) and those in ML-7 treated with tamoxifen were excluded. Overall median follow-up (mfu) was 6.1 y (ML-2, 6.7 y; ML-3, 5.9 y; ML-7, 4.5 y). Given the median PFS of ≈2 y reported with CDK4/6i in 1L ABC, more than doubling that time (PFS >4 y) was considered LTR. VLTR was defined as PFS >5 y, calculated only for postmenopausal pts (ML-2, -3) as mfu in ML-7 was 4 y). Pts with LTR had mPFS of 6.8 y, and mOS was NE. Although LTR was more evident in pts with better prognostic factors, noticeably, some pts with unfavorable prognostic factors were still able to achieve LTR. This exploratory analysis suggests long-term benefit with 1L RIB in keeping a good number of pts with HR+/HER2− ABC free of disease progression for more than 4 y. Citation Format: F. Andre, P. A. Fasching, A. Prat, P. Neven, Y. Lu, A. Bardia, G. Curigliano, V. Kaklamani, P. Razavi, Y. Yap, F. Su, E. Roux, K. Pantoja, J. Wu, A. Lteif, D. Juric. Pooled analysis of patients (pts) treated with 1st-line (1L) ribociclib (RIB) + endocrine therapy (ET) in the MONALEESA (ML) studies: long-term progression-free survival (PFS) [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 PD5-10.