Durvalumab in combination with gemcitabine plus cisplatin is being developed for patients with advanced biliary tract cancer (BTC). BTC is a rare type of cancer that affects bile ducts, which are tubes that link the gallbladder, liver and pancreas together. Bile is produced in the gallbladder and is transported to the small intestine to aid the digestion of fatty foods. Advanced biliary tract cancer is cancer that has grown a considerable amount and/or spread to other areas of the body and is incurable. Chemotherapy using gemcitabine and cisplatin is standard of care for first-line therapy in patients whose cancer is inoperable but the disease has a poor prognosis. There is a need for alternative treatments such as biological therapies. Durvalumab is a drug designed to recognise and attach to a protein called ‘programmed death-ligand 1’ (PD-L1), which is present on the surface of many cancer cells. PD-L1 acts to switch off immune cells that would otherwise attack the cancer cells. By attaching to PD- L1 and blocking its effects, durvalumab increases the ability of the immune system to attack the cancer cells and thereby slow down the progression of the disease. Durvalumab is administered intravenously (IV). If licensed, durvalumab in addition to gemcitabine and cisplatin will offer an additional first line treatment option for advanced BTC.