PDCD1 and neoplasm: In line with these data, although tumor-infiltrating T-cell levels and programmed cell death ligand 1 (PD-L1) expression are the most widely used biomarkers of the response to PD-1 pathway blockade [44,45,46], according to new findings, the mutational burden and tumor-specific neoantigens may also affect how well immunotherapy works by influencing the tumor’s response to ICIs [38].