Used in the treatment of mismatch repair-deficient (dMMR) or microsatellite instability-high (MSI-H) solid tumors, including endometrial cancer and colorectal cancer. It functions by blocking the PD-1 immune checkpoint, thereby enhancing T-cell activation and enabling the immune system to detect and destroy cancer cells more effectively. Approved for use in advanced or recurrent cancers that have progressed after prior therapies. Also being studied in combination with other immunotherapies and chemotherapies to broaden anti-tumor responses across various cancer types.