NTAN1 and neoplasm: Interestingly, expression of the HEV-specific marker, PNAd, is below the level of detection using conventional immunohistochemical staining in some tumours and EC lining HEV expressing low levels of PNAd are flat [25], as opposed to the characteristic, LTβR-dependent cuboidal morphology of HEV in LNs [60] which suggests that they are not fully differentiated.