Confirmation of R132H mutation of isocitrate dehydrogenase 1 as an independent prognostic factor in anaplastic astrocytoma

Abstract

Identification of mutations affecting codon 132 of the enzyme cytosolic isocitrate dehydrogenase 1 (IDH1) in astrocytomas, oligodendrogliomas and secondary glioblastomas has influenced current concepts of diffuse gliomas. A recent study published in this journal demonstrated that in anaplastic astrocytomas and glioblastomas IDH1 mutation status better reflected patient prognosis than histological diagnosis according to the current WHO classification system [3]. Even more intriguingly, patients with IDH1 wild type anaplastic astrocytomas demonstrated not only shorter overall survival (OS) when compared to IDH1 mutant anaplastic astrocytoma patients, but even survived shorter than patients with IDH1 mutant glioblastoma. Results were based on data from the NOA-04 trial [7] and the German Glioma Network [6]. Here, we screened an independent tumor dataset of patients at the Neurooncology Center (Comprehensive Cancer Center Tubingen) consisting of 281 gliomas that were not enrolled in the aforementioned studies for IDH1 R132H mutation using a recently developed monoclonal antibody that has been successfully validated [1]. Patient age (mean: 51 years, range 18–81 years) and survival (Maximum follow-up: 12.5 years, mean 2.3 years) were retrieved from clinical records (Departments of Neurology and Neurosurgery). For all tumor samples, grading was performed by the first three authors (JS, MM, RM), resulting in 39 diffuse astrocytomas grade II, 44 anaplastic astrocytomas grade III and 198 glioblastomas grade IV. Mixed oligo-astrocytic tumors and cases on which the raters did not unanimously agree were not included. Sections were deparaffinized, rehydrated, and immunostained using the Benchmark immunohistochemistry system (Ventana Medical Systems, Tucson, AZ, USA). Slides were incubated with mIDH1R132H hybridoma supernatant for 32 min (clone H09, dilution 1:2, standard Cell Conditioner 2 pretreatment and signal amplification). Cases exhibiting cytoplasmic IDH1 immunoreactivity in tumor cells were considered positive, i.e. carrying the IDH1 R132H mutation (Fig. 1). Statistical testing (ANOVA/ student t for age, Kaplan–Meier survival/Log-rank determination, Parametric survival fit/Weibull distribution) was performed using JMP In 7.0 statistical software (SAS, Cary, NJ, USA). The R132H mutation was present in 18/39 (46%) grade II, 24/44 (55%) grade III and 10/198 grade IV (5%) neoplasms and thus was slightly lower than previously reported (63% for grade II, 58% for grade III [4]). In all WHO grades, patients with IDH1 mutated tumors (mean age: 36 years in grade II, 39 years in grade III and 45 years in grade IV) were significantly younger than patients with J. Schittenhelm (&) R. Meyermann Department of Neuropathology, Institute of Pathology and Neuropathology, University of Tubingen, Tubingen, Germany e-mail: jens.schittenhelm@med.uni-tuebingen.de