Glioblastoma is a primary tumor of the brain with a poor prognosis. Pathological examination shows that this disease is characterized by intra-tumor morphological heterogeneity, while numerous and ongoing genomic analysis reveals multiple layers of heterogeneity. Intra-tumor and patient-to-patient heterogeneity is underpinned by cellular, genetic, and molecular heterogeneity, which is thought to be key determinants of time to tumor recurrence and resistance to therapy. The key cell type believed to contribute to the establishment and ongoing evolution of tumor heterogeneity is a glioma stem cell (GSC) subpopulation. In this chapter, we review, highlight, and discuss controversies and clinical relevance of Glioblastoma heterogeneity and its cellular basis. Characterization of how cancer stem cells (CSCs) behave is important in understanding how tumors are initiated and how they recur following initial treatment.
