Adequate effectiveness of ribociclib plus letrozole or fulvestrant in patients with advanced or metastatic hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer treated in routine Bulgarian clinical practice

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Randomized controlled trials (RCTs) are typically conducted in highly selected patient populations to ideally demonstrate unconfounded clinical efficacy of a drug. In the real world, there may be confounding factors, such as comorbidities or less frequent monitoring. It has therefore become standard practice in many countries to validate findings from RCTs against available real-world datasets. The present analysis investigated a real-world evidence (RWE) cohort of Bulgarian patients treated with ribociclib in combination with letrozole or fulvestrant and compared the clinical benefit rate (CBR, defined as complete remission [CR] or partial remission [PR] or stable disease [SD]) and progression-free survival (PFS) and overall survival (OS) with pivotal RCTs. Data from 812 patients treated between 2018 and 2022 were used. The number of patients at risk was statistically robust to compare PFS and OS during the earlier periods of the real-world data analysis with the corresponding RCTs. Baseline characteristics (age, hormone receptor status, status of newly diagnosed vs. existing, previous treatments, performance status and tumor stage) were largely comparable between the RWE cohort and the RCTs. The RWE cohorts corroborated RCT findings of a CBR benefit of the ribociclib plus letrozole or fulvestrant combination compared to letrozole or fulvestrant alone. In the periods of adequate statistical robustness, PFS and OS were comparable within 95% confidence intervals (CIs) with RCT findings. This analysis found that patients with comparable characteristics use ribociclib in the real-world similarly to what has been investigated in the RCTs. Real-world effectiveness and outcomes of ribociclib combination therapy were comparable with observations from RCTs.