The assessment of PD-L1 in lung cancer using the Tumour Proportion Score (TPS) is one of the cornerstones of immune-oncology, but it is open to inter- and intra-pathologist variation, particularly around the clinical thresholds of less than 1%and ⩾ 50%, which correspond to analytical thresholds less than 5% and between 40%-60%. The gene discussed is CD274; the disease is neoplasm.