NES and central nervous system cancer: This suggests that the glioma cells in PpIX hotspots were growing along established blood vessels, which is termed vessel co-option.33,34 Molecules released by endothelial cells of small blood vessels create perivascular niches, which attract and sustain glioma cells.35–37 Niches have been subdivided on the basis of the signaling mechanisms operating within the niche.38 Our data suggest that the PpIX hotspots in lower-grade gliomas represent an invasive niche involving nestin+ glioma cells, which may proliferate around small blood vessels.