IDH1 and diffuse astrocytoma: Hence, “GBM, isocitrate dehydrogenase (IDH)-wildtype” is defined as a grade 4 adult-type diffuse astrocytoma lacking IDH and histone mutations, with simultaneous gain of chromosome 7 and loss of chromosome 10, epidermal growth factor receptor (EGFR) amplification, TERT promoter mutations, mitoses, necrosis, or microvascular proliferation.