Pembrolizumab is a humanized monoclonal antibody that blocks the interaction between PD-1and its ligands, PD-L1 and PD-L2. It is used for the treatment of several types of cancer such as,Melanoma, Non-Small Cell Lung Cancer and Head and Neck Cancer.Due to its success in clinical trials, pembrolizumab was approved early to allow quick patientaccess and was given breakthrough therapy and orphan drug designation.