Immune Checkpoint Inhibitor Therapy in Hormone Receptor-Positive Breast Cancer

Recent progress in immunotherapy has led to the routine use of immune checkpoint inhibitors (ICIs) in TNBC therapy and significant improvement in clinical outcomes. Incorporation of ICI into HR+/HER2- or HER2+ breast cancer has been hindered by its poor immunogenicity, and many novel combination strategies aim to convert immune cold tumors into immune hot tumors and increase the immunogenicity of HR+/HER2- breast cancer. A few recent clinical trials have shown its potential promise in high-risk HR+/HER2- early-stage breast cancer, but there is insufficient evidence to support routine use of immunotherapy in HR+ breast cancer, and longer-term follow-up is required to understand its impact on survival. This review presents an overview of immunotherapies currently under clinical development and updated key results from clinical trials, with a focus on HR+/HER2- breast cacner.