IDH1 and glioma: When the original investigations of TP53 mutation as a prognostic factor in glioma were published between 1991 and 1999 [26,81,82,83,84,85,86,87,88,89], the molecular classifiers of LGG (1p/19q co-deletion, ATRX loss and IDH1/2 mutations) were not well-established enough to allow LGG sub-typing [90,91,92].