CD274 and neoplasm: In conclusion, our results suggest that increased IL-21-associated inflammation in the tumor milieu may favor Treg-mediated immune evasion through the PD-L1/PD-1 pathway and that the IL-21 neutralization strategy may enhance PD-1 blockade-based tumor immunotherapy by targeting Treg-mediated immune evasion in patients with high expression of IL-21 and PD-L1.