PDCD1 and neoplasm: To solve this problem, several biomarkers have been identified in recent years, including tumor mutational burden (TMB), tumor-neoantigen burden, programmed cell death protein 1 (PD-1) or programmed cell death ligand 1 (PD-L1) expression level, interferon-gamma (IFNγ) signature, and CD8+ T cell infiltration (7–11).