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

Abstract: 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. Keywords: breast cancer, immunotherapy, checkpoint inhibitors, CAR T cells, CAR NK cells, oncolytic viruses, exosomes