Checkpoint inhibitor
Immune checkpoints are normal molecular signals that keep the immune system from attacking the body's own healthy tissue — some tumors exploit these same signals to avoid being attacked. Checkpoint-inhibitor drugs block that signal, releasing the brake so the immune system can recognize and act against the tumor. Whether a checkpoint inhibitor is likely to help depends on biomarker testing (such as PD-L1 expression or MSI-H/dMMR status), not the cancer type alone.