PDCD1 and soft tissue sarcoma: Recently, it was reported that programmed cell death 1 (PD-1), programmed cell death ligand-1 (PD-L1) immune checkpoint mechanism, and cancer-testis antigens, New York esophageal squamous cell carcinoma-1 (NY-ESO-1) and melanoma-associated antigen 4 (MAGE-A4), are involved in the pathogenesis of soft tissue sarcomas (STS).[4,5]