While IDHmut gliomas are enriched for tumors with lower-grade histomorphology, there is no known definitive histologic standard for determining IDH status from histomorphology alone, and immunohistochemical or molecular methods remain the unequivocal gold-standard for such a determination; however, histomorphologic correlates of molecular alterations are well-recognized in many tumor types, including infiltrating gliomas. The gene discussed is IDH2; the disease is neoplasm.