Endothelial cell heterogeneity. a) Development of end-organ EC from EPCs (left) is a multistep process affected by epigenetic factors and microenvironmental factors. Ultimately, the resulting capillary endothelium varies by tissue type. The endothelium can be continuous, fenestrated, or sinusoidal (right). b) The behavior of BMECs and HUVECs vary by source. Sprouting (left) and permeability (right) are less prominent in BMECs versus HUVECs. c) Tumor ECs associated with highly metastatic tumors have enrichment in genes corresponding to invasion, angiogenesis, drug resistance, and stemness. (a) Left: reproduced with permission.[30] Copyright 2007, Lippincott Williams & Wilkins. Right: reproduced with permission.[67] Copyright 2019, Lippincott. (b) Adapted with permission.[29] Copyright 2019, Elsevier.