PROM1 and glioblastoma: Although our analysis has shown significant overlap with CD133+ GSCs, CD133's reliability as a GSC maker has been questionable and the stem-like populations within GBM can also be identified using a variety of other markers.5 Further investigation is needed to understand the role of GPR133 in other stem-like populations within GBM and to test whether GPR133 itself is potentially a GSC marker.