PDCD1 and neoplasm: Notably, different possible biomarkers have been evaluated that can predict responses to immunotherapy: programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) immune checkpoint, tumour mutational burden (TMB), defects in DNA mismatch repair proteins (dMMR) and a subsequent microsatellite instability-high (MSI-H).