HLA-B and cancer: Moreover, unlike the frequent downregulation of major histocompatibility complex (MHC) class I and II genes essential for antigen presentation and activation of the adaptive immune system in ECs evident in malignant tumour tissues,62, 63 MHC class I genes such as human leukocyte antigen A (HLA‐A), HLA‐B and HLA‐C and MHC class II genes such as HLA‐DRA, HLA‐DPA1 and HLA‐DQB1 were expressed at comparable levels in PA and PG ECs (Figure 5F).