Clinical and demographic characteristics and treatment outcomes of patients with HR+/HER2– advanced breast cancer receiving ribociclib in standard clinical practice in Russia: interim results of the PROSPERITY study

Objective. To describe the clinical and demographic characteristics and to assess the effectiveness and safety of ribociclib combined with endocrine therapy (ET) in patients with HR+/HER2– advanced breast cancer (ABC) in Russian clinical practice settings, as part of the PROSPERITY observational study. Materials and methods. At the date of the interim analysis (October 31, 2024), the PROSPERITY study had enrolled 2.390 patients with HR+/HER2– ABC receiving ribociclib, alpelisib, ET, or chemotherapy as part of standard clinical practice in Russia. The ribociclib group comprised 1.468 patients (61.4% of the total cohort). This article analyzes clinical and demographic characteristics, time to treatment failure (TTF), progression-free survival (PFS), overall survival (OS), time to chemotherapy (TTC), and the safety profile of ribociclib. The index date was defined as the date of initiation of ribociclib therapy during the study enrollment period. Results. The median age of patients in the ribociclib arm was 59.0 years. The majority of patients received ribociclib as first-line (63.0%) or second-line (21.9%) therapy. The median TTF was 17.2 months (95% CI 16.1–18.4), and the median PFS was 20.3 months (95% CI 18.8–21.5). Median PFS was 24.3 months for first-line therapy, 16.0 months for second-line, 13.4 months for third-line, and 8.6 months for fourth and subsequent lines. Median OS and median TTC were not reached. Adverse events (AEs) were reported in 47.5% (723/1522) of patients; the most common were neutropenia (16.2%) and leukopenia (7.4%). The rate of treatment discontinuation due to AEs was low (5.9% of all patients in the ribociclib arm). Conclusion. The observational PROSPERITY study provided real-world data from Russia demonstrating ribociclib effectiveness and safety profiles generally comparable to results previously obtained in pivotal clinical trials.