PDCD1 and neoplasm: Although no long-term clinical studies have prospectively evaluated the efficacy of denosumab combined with immune checkpoint inhibitors (ICIs) targeting CTLA4, programmed cell death protein 1 (PD-1), and programmed cell death 1 ligand 1 (PD-L1) in the treatment of tumor bone metastases, some retrospective analyses and case reports have documented the synergistic effect of ICIs combined with denosumab.