IDH1 and glioma: In order to investigate this hypothesis, we systematically reviewed all existing literature on GFAP expression in patient material of astrocytoma (grade I–IV classified according to the WHO 2007 system or earlier), IDH1 wild‐type (IDHwt) glioma, and IDH1 mutated glioma without a 1q19p codeletion (IDHmut noncodel; classified according to the WHO 2016 system).