Cancers can switch off immune attack by exploiting natural “checkpoint” signals (like PD-1/PD-L1 and CTLA-4) that normally keep the immune system from harming healthy tissue. Checkpoint inhibitors are monoclonal antibodies that block those off-switches, freeing T-cells to attack tumor cells. They have transformed treatment of melanoma, lung, kidney, bladder, head-and-neck and other cancers, and can produce long-lasting responses in a subset of patients. Because they rev up the immune system broadly, they can also cause the immune system to attack normal organs (immune-related side effects).
By IV infusion, typically every few weeks in an outpatient clinic, continued for a set period or as long as it helps. Biomarker testing (PD-L1, MSI/MMR, tumor mutation burden) helps predict who is most likely to respond.
Some patients have durable, long-lasting responses. Immune-related side effects can appear at any time and are managed by holding the drug and, if needed, giving corticosteroids — prompt reporting of new symptoms is important.