IDH1 and diffuse astrocytoma: The IDH1 mutation tends to occur in the early stages of gliomagenesis, hence it is most commonly found in low-grade gliomas, diffuse astrocytoma and oligodendrogliomas [1], but is less common (10%) in primary glioblastoma (GBM) [2,3], except where the GBM develops from a previously diagnosed diffuse or anaplastic astrocytoma (>80%) [4,5].