Illustration of the complexity and cellular composition of glioma. Gliomas consist of neoplastic tumor cells and non-neoplastic cells from microenvironment, including endothelial cells, pericytes, infiltrating monocytes, activated astrocytes and TAMs. TAMs are recruited to the tumor by tumor bulk and GSCs. These recruited and reprogrammed TAMs secrete soluble factors that both expand the tumor bulk and GSCs as well. Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2015. All rights reserved.