CA9 and glioblastoma: In GBM, the expression of hypoxia markers (carbonic anhydrase IX [CAIX] hypoxia inducible factor-1 [HIF-1α]) has been shown to be especially high in tumour regions containing 10% to 45% necrosis of total area.15 Additionally, it has been reported that tumour-initiating CD133+ GBM stem cells are preferentially expanded in hypoxic conditions.15,16 Therefore, hypoxia might have also influenced the proportion of CD133+ GBM cells in the present study.