PECAM1 and neoplasm: As predicted from scRNAseq profiles, tissue immunostaining revealed that protein markers of endothelial tip cells associated with capillary sprouting outgrowth, such as Apln (apelin) and Vegfr2 (VEGF receptor 2), were widely expressed among CD31+ cells in MES-GSC83-KO tumours (with disrupted EGFR gene expression).