Evaluation of IDH1 status in diffusely infiltrating gliomas by immunohistochemistry using anti-mutant and wild type IDH1 antibodies

Abstract Glioma cells with the isocitrate dehydrogenase (IDH) 1 G395A mutation are strongly immunopositive for mIDH1R132H, an antibody against mutant IDH1R132H (clone H09). However, we encountered some gliomas which were ambiguously positive for mIDH1R132H despite having the IDH1 G395A mutation. The aim of this study was to establish an evaluation procedure of IDH1 status by immunohistochemistry. Forty-three diffusely infiltrating gliomas were studied, and four of eight anaplastic oligoastrocytomas with the IDH1 G395A mutation were modestly or weakly positive for both the mIDH1R132H and an antibody against wild type IDH1, RcMab-1. Based on our staining results, the IDH1 expression of both wild and mutated types seemed to be codominant and also to be evenly suppressed under a certain condition. We propose a procedure for determining IDH1 status. If a glioma is weakly positive for mIDH1R132H, immunohistochemistry for RcMab-1 should be performed. If the tumor cells are strongly positive for RcMab-1, the IDH1 G395A mutation is judged to be absent on the grounds that IDH1 expression is not suppressed. If the tumor cells are weakly positive for both mIDH1R132H and RcMab-1, then a conclusion should be made after DNA sequencing. This procedure is useful for practical evaluation of IDH1 status.
Source: Brain Tumor Pathology - Category: Neurology Source Type: research