EGF and glioblastoma: In the laboratory, GSC are defined as patient tumor-derived glioblastoma cells expressing normal stem cell markers that are capable of clonal self-renewal and proliferative differentiation to populate tumor spheres in serum-free cultures supplemented with epidermal growth factor (EGF) and fibroblast growth factor (FGF) for indefinite passages (Figure 2A and 2B).