In women with metastatic breast cancer, programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) inhibitors are given as the primary line of monotherapy. However, in patients with hormone receptor-positive metastatic breast cancer (HR-MBC), the benefits of PD-L1 inhibitors are not significant. This study aims to evaluate the efficacy of eribulin with or without pembrolizumab in patients with HR-MBC.

This multicenter, randomized, phase-2 clinical trial included a total of 88 patients with HR-MBC. The patients were randomly assigned in a 1:1 ratio to receive eribulin (combination group) or eribulin alone. The primary outcome of the study was progression-free survival, along with objective response rate (ORR) and overall survival (OS).

During a median follow-up of 10.5 months, median progression-free survival was 4.1 months in the combination group and 4.2 months in the eribulin alone group. The ORR was also the same in the two groups: 27% in the combination group and 34% in the eribulin alone group. All-cause adverse events occurred in all patients in the combination group, including 2 treatment-related deaths.

The research concluded that adding pembrolizumab to eribulin did not improve progression-free survival, ORR, or OS in patients with HR-MBC.