PDCD1 and cancer: Immune checkpoint inhibitors (ICIs) work by disrupting inhibitory pathways that limit the immune system’s ability to recognize and destroy cancer cells, targeting specific immune checkpoints like CTLA-4, PD-1, PD-L1, lymphocyte activation gene 3 (LAG-3), T-cell immunoglobulin and mucin domain-3 (TIM-3), and T-cell immunoglobulin and ITIM (TIGIT) (Figure 1).