Efficacy and safety of cyclin-dependent kinase 4/6 inhibitor in patients with advanced breast cancer: A real-world experience

Background: Cyclin-dependent kinases 4 and 6 inhibitors (CDK4/6i) have been shown to improve progression-free survival (PFS) in patients with metastatic breast cancer (MBC) in randomized control trials. This study aimed to evaluate the efficacy and safety of CDK4/6i in patients with advanced breast cancer (ABC) in a clinical setting. Methods: Consecutive patients with ABC were treated between October 2019 and March 2023 at Taipei Tzu Chi Hospital, Taiwan. Patients who had received at least one dose of CDK4/6i were included in this retrospective study. The main outcome of this study was efficacy based on the treating physicians' assessments in terms of PFS, and overall survival (OS), as well as the factors associated with patient outcome. The secondary outcome was safety. Results: A total of 85 patients were included in the analysis, with a mean age of 66.8 years. After a median follow-up of 16.1 months, the median PFS was 28.4 months (95% CI: 22.5-33.6) and the median OS could not yet be estimated. The most common adverse events (AE) were fatigue (50.8%), anorexia (45.9%), and leukopenia (44.7%). In multivariable analysis, treatment with CDK4/6i with any grade AE or response to treatment effect (CR/PR) was an independent predictor for longer PFS (hazard ratio [HR] = 0.27, 95% CI: 0.11-0.68; HR = 0.21, 95% CI: 0.06-0.67; p < 0.05). Conclusion: CDK4/6i administered in a real-world setting exhibits a similar survival benefit with the clinical trials.