Checkpoint inhibitors are a type of cancer treatment that help the immune system recognize and attack cancer cells. They work by blocking proteins, known as checkpoints, that normally keep immune responses in check. By inhibiting these proteins, the treatment allows immune cells, like T-cells, to become more active against tumors. These therapies have shown promise in treating various cancers, including melanoma and lung cancer. Some common checkpoint inhibitors include pembrolizumab and nivolumab. They are often used in combination with other treatments to enhance their effectiveness and improve patient outcomes.