Pembrolizumab is an immuno-oncology drug administered intravenously that stimulates the body's immune system to fight cancer cells. Pembrolizumab targets and blocks a protein called PD-L1 on the surface of certain immune cells called T-cells. Blocking the PD-L1 protein triggers the T-cells to find and kill cancer cells. Pembrolizumab is already approved for use in other types of cancers. If licensed in the UK, pembrolizumab in combination with chemotherapy would provide a new treatment option for lung cancer patients who currently have a poor life expectancy and few therapies available.