Discordant case #4. Case #4 was IDH1 R132H negative by IHC and was identified as wild-type by Sanger sequencing for IDH1 codon 132. The IDH1/2 PCR assay identified an IDH1 R132C mutation which was confirmed by pyrosequencing. a H&E slide. b IDH1 R132H IHC positive staining. c Sanger sequencing. d the pyrogram indicates the presence of the IDH1 R132C mutation (TGT) at a low allele frequency (around 15%) suggesting that the sample contained low tumor cell content. e PCR-clamping: the difference between the IDH1 PCR-clamping mutation assay Ct (blue curve) and total assay Ct (red curve) is inferior to the cutoff value (ΔCt = 31.87 - 27.49 = 4.38 < 5.34) indicating the presence of a mutation within IDH1 codon 132. f ARMS: the difference between the total assay Ct (red curve) and the IDH1 R132C ARMS assay Ct (green curve) is inferior to the cutoff value (ΔCt = 31.20 – 27.49 = 3.71 < 7.14) indicating presence of the IDH1 R132C mutation.