Prospect of immunotherapy in neoadjuvant/adjuvant treatment for early breast cancer

Immunotherapy is revolutionary and changing the cancer therapy of multiple solid tumors. Immunotherapy began with discovering the proteins of immune checkpoints such as programmed death-1 (PD-1), programmed death ligand-1 (PD-L1) and cytotoxic T-lymphocyte associated antigen-4 (CTLA-4). Breast cancer, unlike cancers with high tumor mutation burden, is generally considered to be of intermediate immunogenicity; therefore, the efficacy of checkpoint monotherapy is limited. Among breast cancer subtypes, triple negative breast cancer (TNBC) is considered to be the most immunogenic and is mainly evaluated in clinical trials. Some trials have demonstrated that checkpoint inhibitors when combined with chemotherapy improve the survival of TNBC patients. When investigating new drugs, a neoadjuvant setting is preferred because drug efficacy can be evaluated earlier using pathological complete response (pCR) as an alternative endpoint for survival. The strategy is based on the accumulated results that pCR after neoadjuvant therapy significantly correlates with both progression free survival (PFS) and overall survival (OS). We aimed to review relevant articles, and discuss the current position of immunotherapy and future prospects of immunotherapy as neoadjuvant/adjuvant therapy in breast cancer based on our conclusions from the findings in the current literature.