Real-world effectiveness of ribociclib in metastatic breast cancer patients: Does dose affect survival?

Introduction: Real-world data are critical to demonstrate the reproducibility of evidence and external generalizability of randomized clinical trials. The purpose of this study was to assess real-world security profile and management of adverse events (AEs) presented with ribociclib for the treatment of HR + /HER2- metastatic breast cancer (MBC). Our secondary objective was to provide real-world effectiveness of this treatment (measured with progression-free survival (PFS)) and to confirm the hypothesis that dose reductions are not related with disease progression. Material and methods: Observational retrospective study evaluating all females with MBC treated with ribociclib. Study period: January 2017 to September 2019. Follow-up was done until November 2021. Response was assessed through the PFS according to RECIST1.1 and National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) was used to classify AEs. Results: The most common AE was any grade neutropenia, documented in 37 of 53 patients (69.8%) during the course of treatment. By the end of the follow-up period, overall median PFS with ribociclib therapy was 27.3 months (95% confidence interval (CI) 20.8-71.8 months). In total, 50 patients (94.4%) initiated ribociclib at 600 mg dose, 28 patients (58%) required dose reductions. PFS of patients receiving ribociclib as first-line treatment was 28 (95% CI 15-41 months). Conclusions: Our results from patients treated in real-world clinical settings indicate that ribociclib is safe and their AEs are manageable with active monitoring, temporal suspension of treatment and dose reduction. Furthermore, our results indicate that dose reduction of ribociclib is not associated with a loss of efficacy.