Immunohistochemical expression of IDH1 in gliomas: A tissue microarray-based approach

Background: Mutations in the gene encoding isocitrate dehydrogenase (IDH1) have been reported in gliomas. This study analyses a series of 184 glioma cases in a tissue microarray (TMA)-based approach to assess the frequency of R132H point mutations in formalin-fixed, paraffin-embedded tissue samples. Materials and Methods: A total of 195 gliomas (30 pilocytic astrocytoma [PA], 45 diffuse astrocytoma [DA], 75 glioblastoma multiforme [GBM], 25 oligodendroglioma [OLIG] and 20 ependymoma [EPEN]). A TMA of core size 1.0 mm was constructed using a semi-automatic tissue arrayer. Immunohistochemical staining for IDH1, p53 and EGFR proteins was performed by the labeled sterptavidin avidin biotin LSAB method. Results: The frequency of mutant IDH1 detection by immunohistochemistry on formalin-fixed, paraffin-embedded tissue was 15.8% in 29/184 tumors found suitable for evaluation. DA, OLIG and GBM showed IDH1 expression in 17/40 (42.5%), 5/22 (22.7%) and 7/72 (9.7%) cases, respectively. Of all the GBMs, prim-GBM showed immunoexpression in 1/7 (1.5%) while sec-GBM showed IDH1 expression in 6/7 (85.7%). PA and EPEN did not react with anti-IDH1 antibody. DA and GBM showed positive correlation with p53, but IDH1 and EGFR coexpression was rare. Conclusion: Monoclonal antibody to IDH1 (R132) is a useful and less-labor-intensive method to detect mutations in gliomas. IDH1 is a useful immunohistochemical marker to differentiate reactive gliosis from low-grade astrocytoma, has potential as an independent prognostic marker and also helps in distinguishing primary from secondary GBM. Its sensitivity and specificity need to be assessed by simultaneous sequencing and its validation on clinically annotated samples.