A Phase 1b Study of Chemo-Immunotherapy with Pegylated Liposomal Doxorubicin and Pembrolizumab in Estrogen Receptor Positive Metastatic Breast Cancer

This phase 1b study evaluated the combination of pegylated liposomal doxorubicin (PLD) and pembrolizumab in 35 patients with estrogen receptor-positive, HER2-negative metastatic breast cancer. The treatment was well tolerated, with minimal hair loss and no significant neutropenia or cardiac events. The disease control rate was 67%, with 10 patients showing responses lasting a median of 11 months, and a median overall survival of 25 months. The study found that pembrolizumab may contribute to the anti-tumor effect, and gene expression profiling identified 16 genes upregulated in responders. The combination therapy is considered active and feasible for extended treatment with durable responses.