48MO Ribociclib (RIB) + Letrozole (LET) in Asian Patients (pts) with Hormone Receptor-Positive (HR+), Human Epidermal Growth Factor Receptor-2–Negative (HER2−) Advanced Breast Cancer (ABC): Subgroup Analysis of the Phase IIIb CompLEEment-1 Trial

CompLEEment-1 is a large phase IIIb trial in an expanded pt population with HR+, HER2– ABC (N = 3,246 pts). Here, we present safety and efficacy data for Asian pts from Hong Kong, India, Malaysia, Philippines, Singapore, Taiwan, and Thailand who participated in the study. Pts with HR+, HER2– ABC, ≤1 line of prior chemotherapy (CT) and no prior endocrine therapy for ABC received RIB + LET. Study design has been reported previously (Lu J. et al, SABCS 2019, Poster P1-19-21). Primary endpoints were safety and tolerability, and secondary endpoint was efficacy. Overall, 197 Asian pts were included (6.1% of the total CompLEEment-1 population); 1.5% pts were male, 84.8% pts were <65 years (median age: 52.0 years), and 34.0% pts were premenopausal. 2.5%, 65.5%, and 12.7% pts had CNS, visceral and bone-only metastasis, 3.6% had prior CT, 5.1% were ECOG2, and 18.3% had relapsed within < 2 years of adjuvant therapy. The median duration of exposure to RIB was 16.1 months, while the median relative dose intensity was 96.9%; 2 patients (1.0%) were lost to follow-up. Adverse events (AEs) and treatment-related AEs occurred in 192 (97.5%) and 177 (89.8%) pts, while grade ≥ 3 AEs and serious AEs were reported in 142 (72.1%) and 45 (22.8%) pts, respectively. The most common all-grade and grade ≥ 3 treatment-related AEs were neutropenia (66.5% and 47.7%), leukopenia (26.4% and 12.7%), and anemia (18.8% and 4.1%). Overall, 74 (37.6%) pts had ≥ 1 dose reduction of RIB; 52 (26.4%) due to AEs. 112 (56.9%) pts permanently discontinued treatment; 15 (7.6%) due to AEs. Median time to progression was 20.3 months (95% confidence interval [CI], 15.5-22.8). For the 156 pts with measurable disease, overall response rate was 44.9% (95% CI, 36.9-53.0%), and clinical benefit rate was 68.6% (95% CI, 60.7-75.8). This subgroup analysis supports the efficacy of RIB + LET in Asian pts for first-line endocrine therapy of HR+, HER2– ABC. The safety profile associated with RIB + LET was manageable with few pts discontinuing treatment due to AEs, consistent with previous phase III trials of RIB + LET.