PDCD1 and breast cancer: Additionally, immune checkpoint biomarkers such as LAG-3 (lymphocyte activation gene-3), PD-1 (programmed cell death protein 1), and PD-L1 (programmed death ligand 1) may also have prognostic value in breast cancer [30,31], and PD-L1 expression on immune cells is being used as a predictive biomarker for immune checkpoint inhibitors in triple-negative breast cancers [32].