Immune Checkpoint Blockade and Emerging Combination Platforms in Breast Cancer: A Narrative Review

This narrative review examines recent progress in immunotherapy for breast cancer (BC), focusing on immune checkpoint inhibitors (ICIs) alone and in combination with other modalities. Landmark trials such as KEYNOTE-522 and IMpassion130 have established the efficacy of pembrolizumab and atezolizumab in triple-negative breast cancer (TNBC). However, BC remains a leading cause of cancer-related fatalities, underscoring the need for novel approaches. We synthesize combination strategies into three mechanistic categories: (I) those that remodel the immunosuppressive tumor microenvironment (chemotherapy, PARP inhibitors, oncolytic viruses); (II) those that enhance effector cell persistence (CAR-T, CAR-NK, cytokine support); and (III) those that modulate immune checkpoint axes beyond PD-1/CTLA-4 (LAG-3, TIM-3, TIGIT). Combining ICIs with CAR-T cells, CAR-NK cells, oncolytic viruses, and exosomes has been shown to improve antitumor immune responses. This review provides a translational framework for biomarker-driven patient stratification and critically evaluates the clinical maturity of emerging platforms. Further research and clinical trials are needed to expand applicability across BC subtypes and improve patient outcomes.