The treatment‐naive or RT‐induced CD109+ GSCs are both highly tumorigenic and radioresistant.21 Other studies showed that PN to MES transition is also associated with global multidrug resistance.16, 17, 44, 55 All these data could therefore explain the poor prognosis associated with the decrease in Olig2 expression that we showed in GBM after adjuvant treatments. This evidence concerns the gene OLIG2 and glioblastoma.