Molecular profile of tumors with oligodendroglial morphology: Clinical relevance

The plethora of biomarkers available for the diagnosis and prognostication of gliomas has refined the classification of gliomas. The new World Health Organization (WHO) 2016 classification integrates the phenotypic and genotyping features for a more robust diagnosis.

Fifty gliomas with oligodendroglial morphology according to the WHO 2007 classification were analyzed for isocitrate dehydrogenase 1 and 2 (IDH1/2) mutations by polymerase chain reaction, 1p/19q status by fluorescent in situ hybridization (FISH), and IDH1 and X-linked alpha-thalassemia retardation (ATRX) expression by immunohistochemistry. Tumors were reclassified into oligodendrogliomas, astrocytomas, and glioblastomas (GBMs) according to the new "integrated" diagnostic approach.

30% of previously diagnosed oligodendrogliomas and almost 90% of oligoastrocytomas were reclassified as astrocytomas. Twenty gliomas showed 1p/19q co-deletion, while 18 gliomas showed polysomy of chromosome 1/19. Polysomy of chromosome 1/19 was significantly associated with astrocytic tumors (P ≤ 0.001). Loss of ATRX expression was seen in 20 of 23 WHO grade II/III astrocytomas and 3 of 7 GBMs. All WHO grade II and III gliomas in our cohort showed IDH1/2 mutations. Moreover, 4 of 7 GBMs showed the wild-type IDH1/2 mutation, and 2 of 3 GBMs which showed IDH1/2 mutations were secondary GBMs. There was no significant difference in progression-free and overall survival between WHO grade II and III gliomas, possibly because all these tumors showed IDH1/2 mutations. In multivariate analysis, only the WHO grade (grade IV versus II and III combined) was significantly associated with increased risk of recurrence and death (P = 0.016 and 0.02).

The new integrated diagnosis provides a more meaningful classification, removing the considerable subjectivity that existed previously.