Discordant case # 1. Case #1 stained IDH1 R132H positive by immunochemistry but was found WT for the IDH1 codon 132 (CGT) by Sanger sequencing, by pyrosequencing and with the IDH1/2 PCR assay a H&E slide. b IHC using the anti-human IDH1 R132H mouse monoclonal antibody DIA clone H09. c Sanger sequencing. d pyrogram indicating an allele frequency of 7%, thus below the cutoff for mutation ≥ 15%. e, f IDH1/2 PCR assay combining PCR-clamping (e) and ARMS (f): the red horizontal lines correspond to the threshold used to determine Ct. Total copies of IDH1 (WT ± mutated) are amplified with the total amplification reaction (red curves) but without further amplification by PCR-Clamping (blue curve) or by ARMS with specific R132H primers (green curve), indicating the absence of any mutation within IDH1 codon 132.