The interaction between programmed cell death protein 1 (PD-1) and its ligand PD-L1 is a core mechanism for tumor immune escape.186–188 Copper can upregulate the expression of PD-L1 in cancer cells through multiple pathways, inhibiting T lymphocytes and inducing exhaustion to facilitate immune escape (Fig. 3d). This evidence concerns the gene PDCD1 and neoplasm.