Emerging immunotherapeutic strategies for the treatment of breast cancer

Immunotherapy has resulted in unprecedented gains in long-term outcomes for many cancer types and has revolutionized the treatment landscape of solid tumor oncology. Checkpoint inhibition in combination with chemotherapy has proven to be effective for the treatment of a subset of advanced triple-negative breast cancer in the first-line setting. This initial success is likely just the tip of the iceberg as there is much that remains unknown about how to best harness the immune system as a therapeutic strategy in all breast cancer subtypes. Therefore, numerous ongoing studies are currently underway to evaluate the safety and efficacy of immunotherapy in breast cancer. In this review, we will discuss emerging immunotherapeutic strategies for breast cancer treatment including the following: (1) Intratumoral therapies, (2) Anti-tumor vaccines, (3) B-specific T-cell engagers, and (4) Chimeric antigen receptor T-cell therapy, and (5) Emerging systemic immunotherapy strategies. For each topic, we will review the existing preclinical and clinical literature, discuss ongoing clinical trials, and highlight future directions in the field.