Case History
A 30 year-old man presents with progressive left side weakness. Imaging shows a right parietal lobe cystic lesion. Testing of the surgical resection specimen demonstrates negative IHC staining for IDH1 (R132H). FISH test is positive for 1p/19q codeletion. What is the next step?
- Sign out as diffuse astrocytoma, WHO grade II.
- Sign out as anaplastic oligodendroglioma, WHO grade III.
- Submit for sequencing (NGS) to confirm IDH status.
- Submit for fusion gene panel.
Answer: C. Submit for sequencing (NGS) to confirm IDH status.
This is an anaplastic oligodendroglioma, WHO grade III. This diagnosis requires demonstration of both IDH mutation and 1p/19q codeletion. Since the IDH1 (R132H) IHC stain is negative, NGS is required in order to confirm the IDH status. In this case, a low frequency IDH2 mutation, R172W, was identified by sequencing, confirming the diagnosis. IDH2 R172W mutation is present in less than 1% of all glioma patients.