Abstract 5270: IDH mutation status and role of WHO grade and mitotic index in overall survival in grade II-III diffuse gliomas

Abstract

Abstract Diffuse gliomas are up till now graded based upon morphology. Recent findings indicate that isocitrate dehydrogenase (IDH) mutation status defines biologically distinct groups of tumors. The role of tumor grade and mitotic index in patient outcome has not been evaluated following stratification by IDH mutation status. To address this, we interrogated 558 WHO grade II-III diffuse gliomas for IDH1/2 mutations and investigated the prognostic impact of WHO grade within IDH-mutant and wild-type tumor subsets independently. The prognostic impact of grade was modest in IDH-mutant [hazard ratio (HR) = 1.21, 95% confidence interval (CI) = 0.91-1.61] compared to IDH-wild type tumors (HR = 1.74, 95% CI = 0.95-3.16). Using a dichotomized mitotic index cut-off of 4/1000 tumor cells, we found that while mitotic index was significantly associated with outcome in IDH-wild type tumors (log-rank p<0.01, HR = 4.41, 95% CI = 2.55-7.63), it was not associated with outcome in IDH-mutant tumors (log-rank p = 0.471, HR = 1.10, 95% CI = 0.80-1.51), and could demonstrate a statistical interaction (p<0.01) between IDH mutation and mitotic index. Patient age, an established prognostic factor in diffuse glioma, was associated with outcome only in the IDH-wild type subset, and consistent with prior data, 1p/19q co-deletion conferred improved outcome in the IDH-mutant cohort. These findings suggest that stratification of grade II-III gliomas into subsets defined by the presence or absence of IDH mutation leads to subgroups with distinct prognostic characteristics. Further evaluation of grading criteria and prognostic markers is warranted within IDH-mutant versus IDH-wild type diffuse grade II-II gliomas as independent entities. Citation Format: Adriana Olar, Khalida Wani, Kristin Diefes, Lindsey Heathcock, Hinke van Thuijl, Mark Gilbert, Terri Armstrong, Erik Sulman, Daniel Cahill, Jaap Reijneveld, Bauke Ylstra, Pieter Wesseling, Kenneth Aldape. IDH mutation status and role of WHO grade and mitotic index in overall survival in grade II-III diffuse gliomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5270. doi:10.1158/1538-7445.AM2015-5270