PDCD1 and breast cancer: The main immune checkpoints for breast cancer include cytotoxic T-lymphocyte-associated protein-4 (CTLA-4), programmed death receptor 1/programmed cell death ligand 1 (PD-1/L1), lymphocyte activation gene 3 (LAG-3), T cell immunoglobulin domain and mucin 3 (TIM-3) and other molecules.