Background: The 2016 World Health Organization (WHO) classification of central nervous system (CNS) tumors has been modified to incorporate the IDH mutation and 1p/19q co-deletion in the diagnosis of diffuse gliomas. In this study, we aimed to evaluate the feasibility and prognostic significance of the revised 2016 WHO classification of CNS tumors in Mongolian patients with diffuse gliomas. Methods: A total of 124 cases of diffuse gliomas were collected, and tissue microarray blocks were made. IDH1 mutation was tested using immunohistochemistry, and 1p/19q co-deletion status was examined using fluorescence in situ hybridization analysis. Results: According to the 2016 WHO classification, 124 cases of diffuse brain glioma were reclassified as follows: 10 oligodendroglioma, IDH mut and 1p/19q co-deleted; three anaplastic oligodendroglioma, IDH mut and 1p/19q co-deleted; 35 diffuse astrocytoma, IDH mut , 11 diffuse astrocytoma, IDH wt , not otherwise specified (NOS); 22 anaplastic astrocytoma, IDH mut , eight anaplastic astrocytoma, IDH wt , NOS; and 35 glioblastoma, IDH wt , NOS, respectively. The 2016 WHO classification presented better prognostic value for overall survival in patients with grade II tumors than traditional histological classification. Among patients with grade II tumors, those with oligodendroglioma IDH mut and 1p/19q co-deleted and diffuse astrocytoma IDH mut showed significantly higher survival than those with diffuse astrocytoma IDH wt , NOS (p < .01). Conclusions: Mongolian diffuse gliomas could be reclassified according to the new 2016 WHO classification. Reclassification revealed substantial changes in diagnosis of both oligodendroglial and astrocytic entities. We have confirmed that the revised 2016 WHO CNS tumor classification has prognostic significance in Mongolian patients with diffuse gliomas, especially those with grade II tumors.

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