Abstract PO3-16-10: Real-world outcomes with first-line ribociclib + endocrine therapy in patients with metastatic HR+, HER2– breast cancer: Fourth interim analysis of REACH AUT trial

Abstract Background: Ribociclib (RIB), a cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) in combination with endocrine therapy (ET) yielded significant improvement in progression-free survival (PFS) and overall survival (OS) across three phase III MONALEESA trials including patients (pts) with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2–) metastatic breast cancer (MBC) in first-line (1L) and second-line (2L) setting. In the previous interim analyses of REACH AUT trial, 1L RIB + ET showed tolerable safety and favorable PFS results in a real-world setting. Results from the preplanned fourth interim analysis are reported here. Methods: REACH AUT is a noninterventional study conducted in Austria reporting data on the real-world clinical experience of RIB + ET (aromatase inhibitor AI or fulvestrant FUL) in premenopausal, perimenopausal, or postmenopausal pts with HR+, HER2– MBC. Pts with no prior ET for advanced disease and maximum up to 1 prior line of chemotherapy (CT) in the advanced setting were included. Results: At data cutoff (March 27, 2023) with a median duration of follow-up of 23.8 months, out of 281 analyzed pts (12.5% of premenopausal/perimenopausal and 85.1% of postmenopausal, 2.5% of unknown status) 31.7% of pts were receiving ongoing treatment. The most common reasons for treatment discontinuations (68.3%) were disease progression (39.1%) and adverse events (AEs, 22.1%). The median age was 63 years ( 65 years, n=156, 55.5%; ≥65 years, n=125, 44.5%) and ECOG PS ≥2: 1.8%. In 106 pts (37.7%), de novo metastatic disease was reported. Visceral metastases (lung, liver) were present in 116 pts (41.3%) and bone-only metastases in 80 pts (28.5%). Prior adjuvant therapy was received by 139 pts (49.5%): AI ± GnRH: n=80 (26.7% without and 1.8% with GnRH); tamoxifen ± GnRH: n=74 (21.7% without and 4.6% with GnRH); CT: n=56 (19.9%); antibody therapy n=3 (1.1%). In the metastatic setting, 1L RIB was prescribed in combination with an AI in 223 pts (79.4%; letrozole: n=139 49.5%; anastrozole: n=48 17.1%; exemestane: n=47 16.7%) and with FUL in 52 pts (18.5%). Prior CT for MBC was received by 5 pts (1.8%). The median PFS was 29.7 months in the overall population; 28.3 months in pts with bone only and 26.9 months in pts with visceral metastatic disease. In pts evaluable for response, the objective response rate and clinical benefit rate were 31.3% and 60.9%, respectively. The OS rates were 91.9%, 81.7%, and 63.7% at 12 months, 24 months, and 36 months, respectively. The trial is ongoing with ~40% of subjects end of documentation and ~27% of deaths. In total, 69.4% of pts had RIB dose interruptions and 48.8% of pts had a RIB dose reduction. The majority of all reported AEs were grade 1 (50.1%) or grade 2 (31.2%); the median time to first AE was 0.5 months. The most common AE was neutropenia (all grades: n=143, 50.9%; grade 1: n=39, 13.9%; grade 2: n=68, 24.2%; grade 3: n=98, 34.9%; grade 4: n=5, 1.8%). QTc prolongation of any grade was observed in 32 pts (11.4%; grade 1: n=24, 8.5%; grade 2: n=11, 3.9%; grade 3: n=1, 0.4%). Hepatobiliary toxicity of any grade was observed in 42 pts (14.9%; grade 1: n=12, 4.3%; grade 2: n=18, 6.4%; grade 3: n=22, 7.8%; grade 4: n=3, 1.1%). Overall, currently 101 pts (35.9%) received a follow-up therapy after progression on RIB + ET. The most common first subsequent therapies were targeted therapies + ET (40.0%), followed by cytotoxic chemotherapy (22.0%) and endocrine monotherapy (19.0%). Conclusion: 1L RIB + ET continues to show favorable efficacy and a tolerable safety profile in the routine clinical practice. The results are consistent with the data from MONALEESA trials. The OS is showing a positive trend but is still immature during this study follow-up. Efficacy Outcomes With RIB + ET in Patients With HR+, HER2– MBC (Overall Population, Nf281) XX XX Citation Format: Christian F. Singer, Daniel Egle, Richard Greil, Edgar Petru, Leopold Oehler, Marija Balic, Laurenz Schöffmann, Georg Pfeiler, Maximilian Marhold, Christine Brunner, Karin Haider, Arik Galid, Ursula Pluschnig, Ferdinand Haslbauer, Michael Hubalek, Andreas Redl, Julia Flatschacher, Shanow Uthman, Bernhard Mraz, Rupert Bartsch. Real-world outcomes with first-line ribociclib + endocrine therapy in patients with metastatic HR+, HER2– breast cancer: Fourth interim analysis of REACH AUT trial abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-16-10.