Neoadjuvant immunotherapy in breast cancer: Progress and challenges.

While breast cancer (BC) has always been considered an immunological 'cold' tumor type, anti-programmed cell death protein 1 (PD-1) has recently changed the treatment landscape of triple-negative breast cancer, and neoadjuvant Phase III trials for high-grade estrogen receptor-positive breast cancer have reported promising results. However, a substantial number of patients do not benefit and are in need of novel combination strategies. In addition, since anti-PD-1 is added to combination chemotherapy, there is a growing issue of overtreatment for patients with an already excellent outcome. In this review, we discuss the status and challenges of neoadjuvant immunotherapy in BC, including the need for prognostic and predictive biomarkers to guide treatment individualization and optimize the balance between the efficacy and toxicity of immunotherapy.