Even more contradictory are the results in C6 glioma cells: Whereas Zhou et al. demonstrated that this cell line contains only a small fraction of cells that can form tumor spheres in serum-free stem cell medium and express stem cell markers CD133 and NESTIN [39], Zheng et al. concluded that the C6 line is mainly composed of CSCs, although many of them are CD133- [40]. The gene discussed is PROM1; the disease is central nervous system cancer.