Figure 5.

R132H IDH1 immunostain identifies admixed non‐neoplastic neurons in gliomas. A 74‐year‐old male underwent incomplete resection for a right frontal lobe mass that contained obvious glioma with mitoses (A, arrow), but also admixed disorganized neurons (C). Within 2 years the patient died from progressive disease. The original tumor was positive for IDH1 mutation on polymerase chain reaction. Mutant R132H IDH1 localization was seen only in the glial elements (B), not the neurons (D, arrows).