NOTCH1 and cancer: Of note, plasma membrane NOTCH1 was uniquely associated with the ablumenal aspect of the endothelium, in direct contact with closely adherent perivascular cells that expressed the HIF-induced non-canonical NOTCH antagonist DLK1, a cancer pericyte-related antigen, together with SMA and PDGFRA (Fig. 5c) [6, 11, 27, 39, 55, 62].