Checkpoint inhibitors are a form of immunotherapy used to treat cancer. They work by blocking proteins that normally keep the immune system from attacking cancer cells, allowing it to recognize and attack the tumor. This type of treatment has been shown to be effective in treating various types of cancers, including melanoma, renal cell carcinoma, non-small cell lung cancer, and bladder cancer. It has also been used in combination with other treatments such as radiation or chemotherapy to improve outcomes. Checkpoint inhibitors can be taken in the form of pills or injections, depending on the type of cancer being treated.