Nevertheless, improving the survival rate of recurrent and metastatic diseases still remains a challenge (less than 30% within two years).2 Immune checkpoint blockade (ICB) is regarded as a promising therapy for numerous solid tumors, including melanoma, non-small cell lung cancer and kidney cancer.3 Recently, immune checkpoint inhibitors that target PD-1 or CTLA-4 have also been tested in OS.4–6 However, only a limited number of patients have demonstrated a response to anti-PD-1 immunotherapy in recent clinical trials. Here, PDCD1 is linked to metastatic neoplasm.