PDCD1 and cancer: Among immunotherapeutic strategies, immune checkpoint blockade (ICB) targeting the programmed cell death protein 1 (PD-1)/PD-1 ligand (PD-L1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4)pathways has demonstrated clinical success in several cancers and is now being actively explored in osteosarcoma (7, 8).