Abstract 3333: Detection of IDH1 R132H mutation in situ in human astrocytoma and glioma FFPE samples

IDH1 and IDH2 mutations have been shown to be early events in gliomagenesis. IDH1 mutations are present in ~33% of gliomas and constitute ~90% of all IDH mutations. Approximately 88% of IDH1 mutations involve the substitution c.395G>A leading to the R132H amino acid change. IDH1 mutations, including R132H, are important to recognize clinically as they are more frequent in younger patients and confer a survival advantage. Patients with IDH1 mutations show lower expression of the prognostic markers p53 and Ki-67 and achieve greater benefit from maximal tumor resection. In addition to their prognostic utility, IDH mutations including IDH1 R132H can be useful as diagnostic markers for low-grade gliomas. In difficult to diagnose glial lesions, the presence of IDH mutations strongly favors a diagnosis of glioma versus reactive gliosis. Although PCR and DNA sequencing-based approaches can detect the IDH1 R132H mutation, these techniques require destruction of tissue for nucleic acid isolation and destroy the morphologic context, highlighting the need for a methodology that can be performed on formalin-fixed, paraffin-embedded (FFPE) tissues. In this study, we developed an assay to specifically detect the IDH1 R132H mutation in FFPE samples in expressed IDH1 mRNA transcripts using the novel Basescope TM technology. IDH1 wild-type (WT) and IDH1 mutation (MT) probes were tested in 6 astrocytoma and 3 glioma FFPE specimens from unique clinical cases. All samples exhibited positivity with the IDH1 WT probe. Two of six astrocytomas and one of three gliomas showed positivity with the IDH1 R132H mutation probe. Among the three positive samples, one astrocytoma exhibited positive signals for the IDH1 R132H mutation in almost all tumor cells, whereas one astrocytoma and one glioma showed only scattered positive signals with the IDH1 R132H mutation probe in a subset of tumor cells. Our findings indicate that the Basescope TM assay is a novel RNA in situ hybridization assay to visualize point mutations in a highly specific and sensitive manner within the morphologic tissue context. In this study, we demonstrate that the Basescope TM IDH1 R132H assay is capable of detecting the IDH1 R132H mutation in routine FFPE clinical specimens for the purpose of assisting in the diagnosis of gliomas and providing prognostic information. The Basescope TM technology also allows for correlation of the frequency and distribution of IDH1 R132H mutations in glial tumors with patient outcomes and overall survival. Citation Format: Na Li, Mindy Wang, Hongzhe Sun, Zhifu Zhang, Xin Wang, Emily Park, Xiao-Jun Ma, Robert Monroe. Detection of IDH1 R132H mutation in situ in human astrocytoma and glioma FFPE samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3333.