PDCD1 and osteosarcoma: In order to further explore and clarify the potential of PD-1 blockade in young sarcoma patients, the expression and clinical association of PD-1, PD-L1 and the presence of CD8+ lymphocytes were assessed in (high-grade) primary untreated tumors (n = 208), consisting of osteosarcoma (n = 46), Ewing sarcoma (n = 32), alveolar rhabdomyosarcoma (n = 20), embryonal rhabdomyosarcoma (n = 77) and synovial sarcoma (n = 22).