Potential and unsolved problems of anti-PD-1/PD-L1 therapy combined with radiotherapy.

Tumor immunotherapy has become one of the main treatments for tumors. Inhibition of the pathways involving programmed cell death receptor 1 (PD-1) and its ligand (PD-L1) has gained favor in anticancer therapy, and can effectively prolong the survival of patients with cancer; however, numerous patients have PD-1/PD-L1 inhibitor primary resistance. The efficacy of anti-PD-1/PD-L1 therapy is related to the host tumor microenvironment. Radiation therapy can promote the body's antitumor immunity, change the tumor microenvironment, and synergize with anti-PD-1/PD-L1 treatment. Preclinical and clinical trials have shown that PD-1/PD-L1 inhibitor combined with radiotherapy has a significant effect. We review the synergistic antitumor mechanism and clinical trials of radiotherapy combined with anti-PD-1/PD-L1 therapy.