Abstract GS1-10: Primary results from the randomized Phase II RIGHT Choice trial of premenopausal patients with aggressive HR+/HER2− advanced breast cancer treated with ribociclib + endocrine therapy vs physician’s choice combination chemotherapy

Abstract Background: Combination chemotherapy (CT) remains a standard of care in advanced breast cancer (ABC) with aggressive disease features (rapidly progressing or highly symptomatic disease, including life-threatening visceral crisis). To date, no data have been published on a head-to-head comparison of CDK4/6 inhibitor (CDK4/6i) + endocrine therapy (ET) vs combination CT in this patient (pt) population. RIGHT Choice, a randomized, open-label, multi-national, Phase II trial, investigated the efficacy and safety of first-line ribociclib (RIB) + ET vs combination CT in pre/perimenopausal pts with HR+/HER2− ABC with aggressive disease (where combination CT is clinically indicated by physician’s judgment). Here we report the results of the primary endpoint of progression-free survival (PFS) and key secondary endpoints from this study. Methods: Pre/perimenopausal pts with HR+/HER2− ABC (>10% estrogen receptor–positive [ER+]) and no prior systemic therapy for ABC were randomized 1:1 to receive either RIB (600 mg daily, 3 weeks on/1 week off) with letrozole/anastrozole + goserelin or investigator’s choice of CT (docetaxel + capecitabine, paclitaxel + gemcitabine, or capecitabine + vinorelbine). Randomization was stratified by presence of liver metastases and whether the disease-free interval (duration from date of complete tumor resection for primary breast cancer lesion to the date of documented disease recurrence) was less than two years. Pts included in the trial had ABC not amenable to curative therapy for which combination CT was clinically indicated by physician’s judgment (i.e., symptomatic visceral metastases, rapid progression of disease or impending visceral compromise, or markedly symptomatic non-visceral disease). Median PFS (mPFS) and median time to treatment failure (mTTF) were evaluated by Kaplan-Meier methods. Overall response rate (ORR) was also analyzed, with quality of life and biomarker analyses planned. RIGHT Choice is registered at ClinicalTrials.gov (NCT03839823). Results: A total of 222 pts (112 RIB + ET; 110 CT) were enrolled from Feb 2019 to Nov 2021. Pts with symptomatic visceral metastases (n=150; 67.6%), rapid disease progression (n=41; 18.5%), and markedly symptomatic non-visceral metastases (n=31; 14.0%) were included. Overall, 116 pts (52.3%) had visceral crisis based on guideline definitions. A majority of pts (n=190; 85.6%) had tumors that were ≥50% ER+. At data cutoff (Apr 12, 2022), median follow-up was 24.1 mo; 45.5% and 23.6% of pts remained on treatment in the RIB + ET arm and combination CT arm, respectively. The primary endpoint was met, with a statistically significant PFS benefit of ≈1 year for RIB + ET vs combination CT (mPFS, 24.0 vs 12.3 mo; hazard ratio, 0.54; 95% CI, 0.36-0.79; P=.0007). OS data were immature at data cutoff. The mTTF was ≈10 mo longer for RIB + ET vs CT (18.6 vs 8.5 mo; hazard ratio, 0.45; 95% CI, 0.32-0.63). The ORR was similar for RIB + ET vs CT (65.2% vs 60.0%). No new safety signals were observed in pts on RIB. Lower rates of treatment-related serious adverse events (AEs; 1.8% vs 8.0%) and lower rates of discontinuation due to treatment-related AEs (7.1% vs 23.0%) were seen with RIB + ET vs CT, respectively. AEs observed with combination CT were consistent with the published data. Conclusions: This analysis demonstrated a statistically significant and clinically meaningful PFS benefit with RIB + ET over combination CT in the first-line pre/perimenopausal pt population with aggressive HR+/HER2− ABC disease. This is the first study comparing a CDK4/6i + ET vs combination CT and demonstrating the superiority of RIB + ET in aggressive HR+/HER2− ABC. This evidence supports RIB+ ET use as a preferred option for this pt population. Citation Format: Yen-Shen Lu, Eznal Izwadi Bin Mohd Mahidin, Hamdy Azim, Yeşim ERALP, Yoon-Sim Yap, Seock-Ah Im, Julie Rihani, James Bowles, Teresa Delgar Alfaro, Jiwen Wu, Melissa Gao, Khemaies Slimane, Nagi El Saghir. Primary results from the randomized Phase II RIGHT Choice trial of premenopausal patients with aggressive HR+/HER2− advanced breast cancer treated with ribociclib + endocrine therapy vs physician’s choice combination chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr GS1-10.