OBJECTIVETo investigate mutation status of isocitrate dehydrogenase (IDH) 1 and IDH2 genes in Chinese patients with gliomas in correlation with clinicopathological characteristics.

METHODSFormalin-fixed and paraffin-embedded (FFPE) tissue samples of 234 gliomas were collected including the matched blood samples in 30 patients. DNA was extracted, followed by PCR-Sanger sequencing to detect IDH1 and IDH2 gene mutations. Immunohistochemistry was performed using mutation-specific antibody recognizing IDH1R132H mutation. Immunostains for p53 and epidermal growth factor receptor (EGFR) were also performed. Oligodendroglial tumors with IDH mutation were double stained with IDH1R132H and GFAP by immunofluorescence to investigate the location of IDH1R132H expression.

RESULTS(1) By IDH1 heterozygous somatic mutation analysis, Arg132His (c: G395A) was found in 31.6% (74 of 234) of the cases. IDH mutations were more frequent in oligoastrocytomas (9/13), anaplastic oligoastrocytomas (7/11), oligodendrogliomas(18/26, 69.2%), anaplastic oligodendrogliomas (8/10), and less frequent in diffuse astrocytomas (17/47, 36.2%), anaplastic astrocytomas (5/18), and glioblastomas (10/69, 14.5%). The mutation rate inversely correlated with the tumor grade in a linear fashion in astrocytic tumors (P = 0.007). Primary glioblastomas were characterized by a lower frequency of mutations than secondary glioblastomas (5/55 vs. 5/14, P = 0.036); IDH mutation was not detected in pilocytic astrocytoma and ependymoma. No IDH2 mutation was identified in this study cohort. (2) Immunohistochemistry of IDH1R132H demonstrated a strong cytoplasmic staining in 80 cases, which was highly correlated with IDH mutation status (P = 0.001). IDH1R132H was highly specific to tumor cells. (3) p53 immunostain was significantly correlated the IDH mutation in diffuse astrocytoma, anaplastic astrocytoma and secondary glioblastomas (P = 0.007, 0.026, 0.038 respectively). (4) No correlation between EGFR and IDH mutation was found.

CONCLUSIONSHigh prevalence of IDH heterozygous somatic mutation occurs in the earlier stage of gliomas, which can be detected by mutation-specific antibody IDH1R132H. Furthermore, evaluation of p53 and EGFR expression combined with IDH mutation analysis may significantly aid in the diagnosis and differential diagnoses of gliomas in Chinese patients.