IDH-1 polymorphisms in pilocytic astrocytomas

As of 2016, isocitrate dehydrogenase (IDH)-1 and IDH-2 mutations are part of the definition of an oligodendroglioma and may be seen in a significant subset of grade II-IV fibrillary astrocytomas. Reports of IDH-1 and IDH-2 alterations in pilocytic astrocytomas have been rare. This study reports two cases of pilocytic astrocytomas which harbored IDH-1 polymorphisms (G105G) (c.315C > T) discovered on polymerase chain reaction (PCR) testing and sequencing. The first was encountered in a 21-year-old male with a right orbital frontal pole mass. The second occurred in a 19-year-old female with a right frontal tumor. Neither tumor stained with antibody to IDH-1 (R132H). No BRAF V600E immunostaining, minimal p53 staining (<5%) and no loss of ATRX staining was noted in both cases. The significance of the IDH-1 findings at this juncture is uncertain. Misdiagnosis of the tumor as a fibrillary astrocytoma or oligodendroglioma due to the presence of an IDH alteration should be avoided.