NES and central nervous system cancer: Nestin is commonly used as a marker for glioma stem/progenitor cells.23 However, nestin is also expressed by other types of activated glial cells, such as reactive astrocytes and activated microglia.24,25 We estimated the PpIX+ cell density attributable to putative glioma cells by subtracting the average contribution of PpIX+ putative endothelial cells from the PpIX+ cell total (Supplementary Methods).