Safety and Efficacy of Ribociclib in Combination with Letrozole in Patients with HR+, HER2− Advanced Breast Cancer: Results from the Italian Subpopulation of Phase 3b CompLEEment-1 Study

BACKGROUND: Ribociclib plus letrozole demonstrated manageable safety and efficacy profiles in hormone receptor–positive (HR+), human epidermal growth factor receptor-2–negative (HER2−) advanced breast cancer (ABC) in the Phase 3b CompLEEment-1 trial. OBJECTIVE: To evaluate the safety and efficacy of ribociclib plus letrozole in the Italian subpopulation with HR+, HER2− ABC from the CompLEEment-1 trial. PATIENTS AND METHODS: Patients with HR+, HER2− ABC received ribociclib (600 mg/day, 3 weeks on/1 week off) plus letrozole (2.5 mg/day) while men and premenopausal women additionally received goserelin. Patients were allowed with ≤ 1 line of prior chemotherapy and an Eastern Cooperative Oncology Group performance status of ≤ 2. The primary outcome included safety and tolerability. RESULTS: Of the 554 Italian patients, 246 (44.4 %) patients completed treatment. The reasons for treatment discontinuation included progressive disease (PD; 36.6 %), adverse events (AEs; 11.9 %), and death (1.6 %). All-grade AEs and grade ≥ 3 AEs occurred in 98.9 % and 77.8 % patients, respectively. The most common treatment-related AEs were neutropenia (73.6 %), followed by leukopenia (32.1 %), and nausea (25.3 %). The overall response rate was 28.2 % (95 % confidence interval [CI], 24.4–32.1); clinical benefit rate was 71.7 % (95 % CI, 67.7–75.4); and median time to progression was 26.7 months (95 % CI, 24.8-non-estimable). Health-related quality of life scores were maintained during treatment. CONCLUSION: The safety and efficacy profiles of ribociclib plus letrozole in the Italian subpopulation was found to be consistent with the CompLEEment-1 global population result, MONALEESA-2, and MONALEESA-7 outcomes, which reaffirm ribociclib plus letrozole as the frontline treatment option in patients with HR+, HER2− ABC. TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION: NCT02941926 (30 November 2016). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11523-022-00913-x.