CD44 and glioblastoma: Podergajs et al. and Wang et al. reported that CD9 is a glioblastoma biomarker that is relevant for the maintenance of glioblastoma stem cells.[37, 38] Other groups, like Jennrich et al., claim that CD9 and CD81 positive EVs are used as biomarkers for glioblastoma, which corroborates their relatively high expression on their parent cells.[39] For the more specific glioblastoma biomarkers, like CD44, CD133, and EGFR, their expression was comparatively lower.