Currently, the best predictive biomarkers of response are the extent of MSI and PD-L1 expression.28 However, although response rates are in excess of 50% in MSI-high tumours, these tumours constitute only ~4% of gastro-oesophageal cancers.28 For this reason, much research has focussed on the expression of PD-L1. This evidence concerns the gene CD274 and neoplasm.