PLD (pegylated liposomal doxorubicin; immunogenic anthracycline) + pembrolizumab (PD-1) posts 67% disease control and 10 responses in heavily pretreated ER+/HER2− mBC

Pegylated liposomal doxorubicin (PLD), a liposomal anthracycline that can induce immunogenic cell death, was combined with pembrolizumab (PEM), an anti–PD-1 checkpoint inhibitor, in a Phase Ib, 2-cohort dose/schedule study in ER-positive/HER2-negative metastatic breast cancer after progression on prior hormonal, biologic, and cytotoxic therapies (n=35). PLD 30 mg/m² Q3W or 40 mg/m² Q4W was given with PEM 200 mg Q3W; disease control rate was 67% with 10 objective responses and a median response duration of 11 months, and median overall survival (OS) was 25 months. Safety appeared manageable (no significant neutropenia, no cardiac events, minimal alopecia), though cutaneous toxicity commonly drove delays after >3 cycles; 3 patients had treatment-related serious AEs—benchmarks for single-agent chemotherapy in similarly pretreated mBC are typically modest (e.g., capecitabine ORR ~26%, time to progression ~4.6 months, OS ~18.1 months in anthracycline/taxane-pretreated populations; eribulin OS ~13.1 months in EMBRACE), so the 11-month response durability and 25-month OS signal is directionally better than historical expectations but needs controlled confirmation.