PDCD1 and cancer: Immune checkpoint inhibitors (ICIs), by blockade immune suppressor components including programmed cell death 1 (PD-1), programmed cell death-ligand 1 (PD-L1), and cytotoxic T lymphocyte antigen 4, have shown antitumor activity in multiple types of cancer.[4] Despite ICIs exhibiting a reduced response rate in breast cancer compared to other malignancies such as lung cancer, melanoma, and head and neck cancer, recent updates from numerous clinical trials suggest that their clinical efficacy may be augmented when used in conjunction with chemotherapy.