Abstract 457: A comparison of IDH1 R132H [H09] and [IHC132] antibodies on diffuse gliomas

Introduction In the 2016 World Health Organization Central Nervous System Tumor Classification, diffuse gliomas were reclassified to include astrocytic tumors (grade II and III), oligodendrogliomas (grade II and III), and grade IV glioblastomas with diffuse astrocytoma being distinct from the diffuse gliomas. This reclassification is due to the abundance of IDH1 mutations in many of these tumors. A much better outcome has been observed in these patients than those without this mutation. IDH1 mutation of the R132H type constitutes more than 90% of all IDH1 and IDH2 mutations. Further, IDH1 IHC is now widely applied for the differential diagnosis of these tumors. There are two distinct IDH1 R132H clones on the market, the H09 and IHC132. Comparing these markers for the IDH1 R132H mutations by IHC can help determine if one is superior for diagnostics. Materials and Methods IHC was performed on 3-5 um thick formalin-fixed, paraffin-embedded (FFPE) brain tissue arrays containing glioblastoma, astrocytoma, oligoastrocytoma, oligodendroglioma with adjacent normal tissue (US Biomax, Derwood, USA). These slides were deparaffinized, and peroxidase blocked in the usual manner. Slides were then subjected to HIER in a pressure cooker using a citrate-based buffer at 110°C for 15 minutes before being stained on a semi-automated instrument. The slides were stained with rabbit monoclonal IDH1 R132H antibody H09 (Dianova, Hamburg, Germany) and mouse monoclonal IDH1 R132H antibody IHC132 (GenomeMe, Richmond, Canada) at concentrations and protocols predetermined to match staining intensity. Results The mouse monoclonal anti-IDH1 R132H IHC132 has shown that it is analogous to the current IDH1 R132H [H09]. Upon review of the data, IHC132 marker stains a higher percentage of cases in glioblastoma compared to H09 (11%, n=36) and equal in astrocytoma (73%, n=15), oligoastrocytoma (75%, n=4), oligodendroglioma (100%, n=8). Neither clone stained normal brain tissue per negative controls. Conclusion Mouse monoclonal anti-IDH1 R132H [IHC132] compared with that of the rabbit monoclonal anti-IDH1 R132H [H09] showed equal sensitivity for astrocytoma, oligodendroglioma, and oligoastrocytomas with higher sensitivity for glioblastoma. The results provide evidence to support a higher percentage of positive staining and equal or greater intensity for clone IHC132 versus H09. Citation Format: Sara Figueroa, Joseph Vargas, Jason Ramos. A comparison of IDH1 R132H [H09] and [IHC132] antibodies on diffuse gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 457.