The fact that the extent of MET and its consequent effect on PD-L1 levels are hysteretic in nature (i.e. cells do not return to their pre-EMT starting point) can possibly explain why tumours at metastatic sites which have undergone a cycle of EMT and MET can show lower levels of PD-L1 as compared to primary tumours (14, 15). This evidence concerns the gene CD274 and neoplasm.