IDH1 and pilocytic astrocytoma: The prevalence of IDH1/2 mutations in gliomas greatly varies depending on the subtypes of tumors; about 70% of astrocytomas of WHO grade II and III carry IDH1/2 mutations, whereas other gliomas such as ependymomas of grade II or pilocytic astrocytomas of grade I do not carry IDH mutations [2, 3, 8].