Fig. 3.

Normal and cancer stem cell (CSC) niches. a The normal stem cell niche includes endothelial cells, stem cells, and stromal cells, with only few inflammatory cells; the stem cells are located near blood vessels, and the inner surface of blood vessels is lined by endothelial cells covered by pericytes. b Vascular CSC niche includes vasculogenic tumor cells, cancer-associated stromal cells, endothelial cells, and other cells. The vasculogenic tumor cells include precancerous stem cells, CSCs, and differentiated tumor cells; vasculogenic CSCs in the tumor blood vessel wall can migrate to the niche and undergo proliferation and differentiation