Tolaney SM, Barroso-Sousa R, Keenan T, et al. - Researchers investigated the efficacy of eribulin plus pembrolizumab vs eribulin alone in patients with hormone receptor–positive/ERBB2-negative metastatic breast cancer (MBC). They conducted a multicenter phase 2 randomized clinical trial including 88 patients. Participants received received eribulin, 1.4 mg/m² intravenously, on days 1 and 8 plus pembrolizumab, 200 mg/m² intravenously, on day 1 of a 21-day cycle or eribulin alone. No improvement in progression-free survival, objective response rate, or overall survival was observed with the addition of pembrolizumab to eribulin vs eribulin alone in either the intention-to-treat or PD-L1–positive populations. Patients receiving pembrolizumab and eribulin had median progression-free survival of 4.1 months vs 4.2 months observed in patients receiving eribulin alone. These outcomes do not support using pembrolizumab in combination with eribulin for these patients.