A combination of tumor morphology, IDH status, and the immunophenotype for IDH1-R132H and ATRX, aided by p53, is adequate to classify most diffusely infiltrating gliomas, with confirmatory assessment of 1p/19q status in suspected oligodendrogliomas and sequencing of the IDH genes to detect suspected non-canonical alterations, and these modalities can be applied in a sequential or algorithmic approach [71, 72]. The gene discussed is IDH1; the disease is neoplasm.