CTLA4 and osteosarcoma: Several novel immunotherapeutic approaches have been evaluated for the treatment of sarcomas, including osteosarcoma, such as monoclonal antibodies directed against the immune checkpoint protein targets cytotoxic T‐lymphocyte antigen‐4 (CTLA‐4) and programmed death‐1 (PD‐1).1, 11, 12, 13, 14