CA9 and glioblastoma: Analyses of the nine human GBM biospecimens for GPR133 expression with the rabbit polyclonal antibody revealed staining in areas of PPN, which are hypoxic and stain positive for the hypoxia markers Hif1α and carbonic anhydrase 9 (CA9) (Figures 2ai–iv).33 All samples also showed overlap between CD133 and GPR133 expression (Supplementary Figure 3ai).