There exist three distinct phase II clinical trials with regards to checkpoint inhibitors on osteosarcoma patients at present; one using anti-PD-1 antibody Pembrolizumab (NCT02301039), and the other two assessing anti-PD-1 antibody Nivolumab without or with anti-CTLA-4 antibody Ipilimumab (NCT02304458 and NCT02500797). The gene discussed is PDCD1; the disease is osteosarcoma.