Pembrolizumab, sold under the brand name Keytruda, is a humanized antibody used in cancer immunotherapy that treats melanoma, lung cancer, head and neck cancer, Hodgkin lymphoma, stomach cancer, cervical cancer, and certain types of breast cancer. It is an IgG4 isotype antibody that blocks a protective mechanism of cancer cells and thereby, allows the immune system to destroy them. It targets the programmed cell death protein 1 (PD-1) receptor of lymphocytes. Pembrolizumab was approved for medical use in the United States in 2014. The product is produced from serum of some rabbits immunized with Pembrolizumab. It is specific for Pembrolizumab. This antibody serves as an excellent positive control for Pembrolizumab immunogenicity (ADA) assays.