IDH1 and giant cell glioblastoma: GS is classified as an IDH-wildtype variant along with giant cell glioblastoma and epithelioid glioblastoma [3]. Histologically, necrosis and endothelial proliferation must be present for the diagnosis of high-grade glioma, and specifically, for diagnosis of GS, tumors must show both glial and mesenchymal differentiation.