PROM1 and isolated hemihyperplasia: A rare subset (0.1–2%) of IH cells that express endothelial cell markers (such as platelet endothelial cell adhesion molecule-1 [PECAM-1/CD31], vascular endothelial-cadherin [VE-cadherin/CD144], CD34, and KDR/VEGFR-2/CD309 co-express the CD133 stem cell marker6.