Durvalumab is an investigational human monoclonal antibody directed against programmed death ligand-1 (PD-L1). PD-L1 can be expressed by tumours to evade detection by the immune system through binding to PD-1 on cytotoxic T lymphocytes. Durvalumab blocks the PD-L1 interaction with PD-1, countering the tumour's immune-evading tactics. Durvalumab is being developed, alongside other immunotherapies, to strengthen the patient's immune system and attack the cancer.