A propensity score–weighted study comparing a two- versus four-weekly pegylated liposomal doxorubicin regimen in metastatic breast cancer

Purpose A 4-weekly schedule of pegylated liposomal doxorubicin (PLD) has been approved for the treatment of metastatic breast cancer (MBC). Phase II trials have suggested interest in a 2-weekly regimen. This study aimed to compare the efficacy and safety of these two schedules. Methods Data from MBC patients treated with PLD between 2011 and 2021 were retrospectively collected. The objective was to demonstrate the noninferiority of the 2-weekly versus the 4-weekly schedule in terms of 6-month progression-free survival (PFS). The prespecified noninferiority margin was calculated as 1.20. A propensity score to receive either schedule was estimated using a gradient boosting algorithm. Survival analyses using Cox regression models weighted by the propensity score were performed to compare the schedules. Results Among the 192 patients included, 96 (50%) underwent each schedule. The median number of previous systemic therapies was 4 (IQR, 3 to 6). Anthracyclines were previously given in early breast cancer in 63.9% of patients. The median follow-up was 10.0 months (IQR, 5.0 to 20.1). A comparable distribution of adverse events was observed. The median PFS was 3.2 months (95% CI, 2.9 to 3.9), and the median overall survival was 12.1 months (95% CI, 10.8 to 14.9). The weighted hazard ratio for PFS was 1.12 (90% CI, 0.82 to 1.54), including the noninferiority boundaries. Conclusion PLD appeared to be a well-tolerated drug in this heavily pretreated MBC population. The efficacy and safety of the 2-weekly schedule did not provide any advantage, suggesting no interest in changing the registered regimen.