PDCD1 and sarcoma: In the sarcoma microenvironment, different cells and cytokines of the immune system may be included, such as tumour infiltrating lymphocytes (TILs) and associated macrophages, expression of immune checkpoint inhibitors such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death-1 (PD-1), and programmed death-ligand 1 (PD-L1), and major histocompatibility complex (MHC) antigen expression [126].