PDCD1 and cancer: However, tumors exploit these pathways by expressing checkpoint proteins like CTLA-4, PD-1, and its ligand (PD-L1), which help cancer cells evade immune detection and promote T-cell exhaustion.9, 10, 11 ICIs targeting checkpoint proteins have shown significant success in cancers such as melanoma, non-small-cell lung cancer (NSCLC), and bladder cancer (BC).12, 13, 14 Despite these successes, response rates remain variable, and not all patients benefit from these therapies.