IDH1 and astrocytoma (excluding glioblastoma): Recent genome-wide mutational analyses have demonstrated the presence of isocitrate dehydrogenase 1 (IDH1) mutations in more than 70% of WHO grade II and III astrocytomas, oligodendrogliomas, and secondary glioblastomas (GBMs) [2, 3], whereas fewer than 5% of primary GBMs harbor this mutation [4].