First, the heterogeneity and variability of PD-L1 expression within individual tumours may account for a limited external validity of our study, knowing that up to 35% of patients may be misclassified based on PD-L1 staining performed on small biopsy samples.36–39 Second, it is known that tumour PD-L1 expression levels can vary over time and be influenced by several host and environmental factors, such as TNM stage, chemotherapy and cytokines like interferon-α.40–43 In our study, both ACT and BCT biopsies were included. This evidence concerns the gene CD274 and neoplasm.