LGG-01. BRAF V600E MUTANT OLIGODENDROGLIOMA-LIKE TUMORS WITH CHROMOSOMAL INSTABILITY IN ADOLESCENT AND YOUNG ADULT

Abstract

We performed genome-wide methylation analysis on 136 pediatric low grade gliomas, identifying a unique cluster consisting of BRAF V600E mutant tumors with chromosomal instability, including gain of Chromosome 7 and loss of Chromosome 10. The tumors were all located in the temporal lobe. Patients presented between 10 and 36 years of age, most with a history of seizures. All patients are alive with no recurrence, three with longer-term follow-up (3.2 to 13.2 years). Microscopically, all showed oligo-dendroglioma-like features, including round nuclei with perinuclear halos, a chicken-wire pattern of branching capillaries and microcalcification. None showed astrocytic features or characteristics suggestive of high-grade tumors including necrosis or mitotic fgures. Copy number analysis showed whole chromosomal copy number abnormalities in more than 10 chromosomes in each case, however none showed 1p/19q co-deletion. IDH1 was wild-type in all cases and one showed a TERT promoter mutation. Although the series is small, these cases demonstrate a new category of IDH wild-type low grade gliomas which may be confused with "molecular GBM". Further, they highlight the heterogeneity of IDH wild-type gliomas and the relatively indolent behavior of "pediatric-type" gliomas.