In case of glioblastoma (GBM), a plethora of such markers, including Prominin (CD133), stage-specific embryonic antigen 1 (CD15), Integrin α6 (ITGA6), CD44, Ephrin A2 (EphA2), Ephrin A3 (EphA3) and myeloid elf-1-derived factor (MEF), has been proposed.7, 8, 9, 10, 11, 12, 13 However, surface marker-negative GBM cells are also able to effectively initiate tumor growth, and therefore, great caution is recommended when designating a marker-positive cell as a GBM stem cell (GSC).11, 14, 15. The gene discussed is PROM1; the disease is glioblastoma.