Keith Kerr, BSc, MB, ChB, FRCPath, FRCPE from the University of Aberdeen, Aberdeen, UK discusses the questions surrounding PD-L1 testing in non-small cell lung cancer (NSCLC). PD-L1 immunohistochemistry testing is being developed in order to help make informed clinical decisions about prescribing appropriate immunotherapeutic agents. Not all patients respond to PD-1/PD-L1 inhibitor treatment and prior PD-L1 testing should be predictive of this so that patients can be selected for treatment. Moreover, if prescribed incorrectly, it can be damaging to the patient as these drugs are somewhat toxic. Recorded at the annual meeting of the European Lung Cancer Conference (ELCC) 2017, Geneva, Switzerland.