Molecular classification and stratification of adult diffuse gliomas: A tertiary care center study.

Background: Diffuse gliomas in the adult population are the most common primary central nervous system (CNS) tumors. The World Health Organization incorporated isocitrate dehydrogenase (IDH) mutations and 1p/19q co-deletion with histopathological features into an "integrated diagnosis" in the revised classification of tumors of CNS. These molecular subgroups of diffuse gliomas are found to stratify patients into prognostically distinct groups better than the histological classification. The objectives of the current study were to assess the frequency of IDH mutation, ATRX expression loss, p53 overexpression, and 1p/19q co-deletion detection in adult diffuse gliomas (Grade II, III, and IV) and to correlate them with clinicopathological and histopathological features.

Materials and methods: The current study was a tertiary care hospital-based retrospective case series of 112 cases of adult diffuse gliomas. Immunohistochemistry (IHC)-based molecular detection was performed for IDH-1, ATRX, and p53 and fluorescent in situ hybridization (FISH) was performed for 1p/19q co-deletion detection.

Results: IDH-1 mutation was present in 30.4% (n = 34/112) cases, ATRX expression was lost in 18% (n = 19/104) cases, p53 was mutated in 39.3% (n = 42/107) cases and 1p19q was co-deleted in 25% (n = 4/16) cases. In the IDH1 mutant cases, with retained ATRX, FISH for 1p/19q co-deletion was performed and was co-deleted in four cases.

Conclusion: The results of the present study indicate that IHC including IDH1/2, ATRX, and p53 is useful for the molecular classification of diffuse gliomas, which could be useful for the evaluation of prognosis, especially Grade III and II. Although the immunohistochemical approach does not replace genetic testing completely, it is a practical and powerful means of assessing molecular genetic changes. IDH mutations are the established markers of better prognosis in diffuse gliomas.