PDCD1 and neoplasm: Ample evidence supports programmed death-ligand 1 (PD-L1) or programmed cell death-1 (PD-1) expression, tumor mutational burden (TMB), numbers of tumor-infiltrating lymphocytes (TILs), peripheral blood lymphocyte count, mismatch repair deficiency (dMMR), and microsatellite instability-high (MSI-H) as predictive biomarkers that guide the clinical application of immune checkpoint blockade (ICB) therapies [7].