High-grade gliomas with isocitrate dehydrogenase wild-type and 1p/19q codeleted: Atypical molecular phenotype and current challenges in molecular diagnosis.

Glioma is the most common intracranial malignant tumor, with poor prognosis. The new World Health Organization (WHO) integrated classification (2016) for diffuse glioma is mainly based on the status of the isocitrate dehydrogenase (IDH) gene (IDH) mutation and 1p/19q codeletion, with diffuse glioma separated into three distinct molecular categories: chromosome 1p/19q codeletion/IDH mutant, 1p/19q intact /IDH mutant, and IDH wild-type. Gliomas harboring 1p/19q codeletion but without IDH mutation are rare and cannot be classified according to the new revision of the WHO classification. Here we report three high-grade gliomas with this atypical molecular phenotype, and describe their histological and immunohistochemical features, the status of mutations in TERT promopter, H3F3A, HIST1H3B, and BRAF, as well as MGMT promoter methylation, and prognosis. Considering morphology, molecular parameters, and patients prognosis, we found that high-grade gliomas harboring 1p/19q codeletion but without IDH mutation were not typical glioblastoma multiforme (GBM) but were more likely to be GBM than anaplastic oligodendroglioma.
(© 2020 Japanese Society of Neuropathology.)