Immunohistochemical analysis of 1844 human epithelial and haematopoietic tumours and sarcomas for IDH1R132H mutation

Characterization of an IDH1 R132H Rabbit Monoclonal Antibody, MRQ-67, and Its Applications in the Identification of Diffuse Gliomas

The current diagnosis of diffuse glioma involves isocitrate dehydrogenase (IDH) mutation testing. Most IDH mutant gliomas carry a G-to-A mutation at IDH1 position 395, resulting in the R132H mutant. R132H immunohistochemistry (IHC), therefore, is used to screen for the IDH1 mutation. In this study, the performance of MRQ-67, a recently generated IDH1 R132H antibody, was characterized in comparison with H09, a frequently used clone. Selective binding was demonstrated by an enzyme-linked immunosorbent assay for MRQ-67 to the R132H mutant, with an affinity higher than that for H09. By Western and dot immunoassays, MRQ-67 was found to bind specifically to the IDH1 R1322H, with a higher capacity than H09. IHC testing with MRQ-67 demonstrated a positive signal in most diffuse astrocytomas (16/22), oligodendrogliomas (9/15), and secondary glioblastomas tested (3/3), but not in primary glioblastomas (0/24). While both clones demonstrated a positive signal with similar patterns and equivalent intensities, H09 exhibited a background stain more frequently. DNA sequencing on 18 samples showed the R132H mutation in all IHC positive cases (5/5), but not in negative cases (0/13). These results demonstrate that MRQ-67 is a high-affinity antibody suitable for specific detection of the IDH1 R132H mutant by IHC and with less background as compared with H09.

Comparative study of IDH1 mutations in gliomas by immunohistochemistry and DNA sequencing

BACKGROUND

Mutations involving isocitrate dehydrogenase 1 (IDH 1) occur in a high proportion of diffuse gliomas, with implications on diagnosis and prognosis. About 90% involve exon 4 at codon 132, replacing amino acid arginine with histidine (R132H). Rarer ones include R132C, R132S, R132G, R132L, R132V, and R132P. Most authors have used DNA-based methods to assess IDH1 status. Preliminary studies comparing imunohistochemistry (IHC) with IDH1-R132H mutation-specific antibodies have shown concordance with DNA sequencing and no cross-reactivity with wild-type IDH1 or other mutant proteins. The present study compares results of IHC with DNA sequencing in diffuse gliomas.

MATERIALS AND METHODS

Fifty diffuse gliomas with frozen tissue samples for DNA sequencing and adequate tissue in paraffin blocks for IHC using IDH1-R132H specific antibody were assessed for IDH1 mutations.

RESULTS

Concordance of findings between IHC and DNA sequencing was noted in 88% (44/50) cases. All 6 cases with discrepancy were immunopositive with DIA-H09 antibody. While in 3 of these 6 cases, DNA sequencing failed to reveal any mutations, R132L (arginine replaced by leucine) mutation was found in the rest 3 cases. Interestingly, of the immunopositive cases, 46.6% (14/30) showed immunostaining in only a fraction of tumor cells.

CONCLUSIONS

IHC is an easy and quick method of detecting IDH1-R132H mutations, but there may be some discrepancies between IHC and DNA sequencing. Although there were no false-negative cases, cross-reactivity with IDH1-R132L was seen in 3, a finding not reported thus far. Because of more universal availability of IHC over genetic testing, cross-reactivity and staining heterogeneity may have bearing over its use in detecting IDH1-R132H mutation in gliomas.

Diagnostic implications of IDH1-R132H and OLIG2 expression patterns in rare and challenging glioblastoma variants

Recent work has demonstrated that nearly all diffuse gliomas display nuclear immunoreactivity for the bHLH transcription factor OLIG2, and the R132H mutant isocitrate dehydrogenase 1 (IDH1) protein is expressed in the majority of diffuse gliomas other than primary glioblastoma. However, these antibodies have not been widely applied to rarer glioblastoma variants, which can be diagnostically challenging when the astrocytic features are subtle. We therefore surveyed the expression patterns of OLIG2 and IDH1 in 167 non-conventional glioblastomas, including 45 small cell glioblastomas, 45 gliosarcomas, 34 glioblastomas with primitive neuroectodermal tumor-like foci (PNET-like foci), 23 with an oligodendroglial component, 11 granular cell glioblastomas, and 9 giant cell glioblastomas. OLIG2 was strongly expressed in all glioblastomas with oligodendroglial component, 98% of small cell glioblastomas, and all granular cell glioblastomas, the latter being particularly helpful in ruling out macrophage-rich lesions. In 74% of glioblastomas with PNET-like foci, OLIG2 expression was retained in the PNET-like foci, providing a useful distinction from central nervous system PNETs. The glial component of gliosarcomas was OLIG2 positive in 93% of cases, but only 14% retained focal expression in the sarcomatous component; as such this marker would not reliably distinguish these from pure sarcoma in most cases. OLIG2 was expressed in 67% of giant cell glioblastomas. IDH1 was expressed in 55% of glioblastomas with oligodendroglial component, 15% of glioblastomas with PNET-like foci, 7% of gliosarcomas, and none of the small cell, granular cell, or giant cell glioblastomas. This provides further support for the notion that most glioblastomas with oligodendroglial component are secondary, while small cell glioblastomas, granular cell glioblastomas, and giant cell glioblastomas are primary variants. Therefore, in one of the most challenging differential diagnoses, IDH1 positivity could provide strong support for glioblastoma with oligodendroglial component, while essentially excluding small cell glioblastoma.

Detection of the BRAF V600E mutation in serous ovarian tumors: a comparative analysis of immunohistochemistry with a mutation-specific monoclonal antibody and allele-specific PCR

Mutations of components of the mitogen-activated protein kinase pathway, mainly BRAF, are common in serous ovarian borderline tumors, whereas high-grade serous ovarian carcinomas rarely show this feature. With the advent of specific kinase inhibitors active against BRAF-mutated cancers, rapid and sensitive detection of the BRAF V600E, by far the most common mutation of this gene, is of great practical relevance. Currently, BRAF mutations are detected by DNA-based techniques. Recently, a monoclonal antibody (VE1) specific for the BRAF V600E protein suitable for archival tissues has been described. In this study, we compared detection of the V600E mutation in serous ovarian tumors by VE1 immunostaining and by allele-specific polymerase chain reaction. All 141 cases of high-grade serous ovarian cancer showed negative or rarely weak, diffuse background VE1 immunostaining, and BRAF wild type was confirmed by molecular analysis in all tested cases. In contrast, 1 (14%) of 7 low-grade serous carcinomas and 22 (71%) of 31 serous borderline tumors revealed moderate to strong VE1 positivity. Immunostaining was clearly evaluable in all cases with sufficient tumor cells, and only rare cases with narrow cytoplasm were difficult to interpret. The V600E mutation was confirmed by allele-specific polymerase chain reaction and sequencing in all VE1-positive cases. Two VE1-positive cases with low epithelial cell content required repeat microdissection to confirm the presence of the mutation. Immunohistochemistry with the VE1 antibody is a specific and sensitive tool for detection of the BRAF V600E mutation in serous ovarian tumors and may provide a practical screening test, especially in tumor samples with low epithelial content.

Mutational analysis of PIK3CA, JAK2, BRAF, FOXL2, IDH1, AKT1 and EZH2 oncogenes in sarcomas

Recent studies have revealed several recurrent mutations in oncogenes that could not only be underlying mechanisms of tumorigenesis, but also be potential targets for cancer therapies. Compared to carcinomas, genetic alterations of sarcomas are relatively unknown. To see whether recurrent oncogenes discovered in non-sarcomatous malignancies are present in sarcomas as well, we analyzed oncogenes with known mutations in various types of sarcomas. We performed mutational analysis of recurrent mutation sites of PIK3CA (exons 9 and 20), JAK2 (exon 14), BRAF (exon 15), FOXL2 (exon 1), IDH1 (exon 4), AKT1 (exon 3), and EZH2 (exon 16) genes in 108 sarcomas by single- strand conformation polymorphism and DNA sequencing. The sarcomas consisted of malignant fibrous histiocytomas, rhabdomyosarcomas, osteosarcomas, malignant peripheral nerve sheath tumors, leiomyosarcomas, synovial sarcomas, liposarcomas, angiosarcomas, chondrosarcomas, and Ewing sarcomas. Overall, we detected the two PIK3CA mutations and one JAK2 mutation (total: 3/108: 2.8%). Two rhabdomyosarcomas (16.7%) and one angiosarcoma (16.7%) harbored the mutations, whereas other sarcomas harbored none. The PIK3CA mutations were novel missense mutations that had not been detected in other cancers. The JAK2 mutation was an intron mutation. This study demonstrated that the somatic mutations of PIK3CA and JAK2 occurred in a small fraction of the sarcomas and that these mutations may not play a principal role in the development of sarcomas.

Detection of 2-hydroxyglutarate in formalin-fixed paraffin-embedded glioma specimens by gas chromatography/mass spectrometry

Mutations in the isocitrate dehydrogenase (IDH) 1 and 2 genes occur frequently in diffuse astrocytoma and oligodendroglioma. The consecutive amino acid substitutions in the mutant proteins result in a gain of the function to catalyze the reduction of alpha-ketoglutarate to 2-hydroxyglutarate (2HG). So far, all investigated IDH mutations share this gain of function. We here describe a method to detect 2HG levels in archival formalin-fixed paraffin-embedded tumor specimens by stable isotope dilution using gas chromatography followed by mass spectrometry (GC/MS). While 2HG levels are notably decreased during the routine embedding process, preserved amounts are still sufficient to indicate a mutation. Detection of 2HG in archival specimens could make routinely processed tissue accessible for research on 2HG accumulation and may allow studies on correlation with clinical data.

Mutation-specific IDH1 antibody differentiates oligodendrogliomas and oligoastrocytomas from other brain tumors with oligodendroglioma-like morphology

Isocitrate dehydrogenase 1 (IDH1) mutations are frequent in astrocytomas, oligoastrocytomas and oligodendrogliomas. We previously reported the generation of a mutation-specific antibody that specifically detects R132H mutated IDH1 protein (clone H09). Here, we investigate the feasibility of H09 immunohistochemistry to differentiate between oligodendrogliomas/oligoastrocytomas and other tumors with similar morphology. A total of 274 brain tumors presenting with focal or extensive clear cell morphology were investigated. High numbers of H09-positive cases were observed in adult grade II oligodendrogliomas (67 of 74, 91%), grade III oligodendrogliomas (65 of 69, 94%), grade II oligoastrocytomas (11 of 14, 79%) and grade III oligoastrocytomas (10 of 11, 91%). All cases of pediatric oligodendrogliomas (n = 7), neurocytomas (n = 41, 35 central, 4 extraventricular, 2 cerebellar liponeurocytomas), dysembryoplastic neuroepithelial tumors (n = 21), clear cell ependymomas (n = 8), clear cell meningiomas (n = 9) as well as 12 primary glioblastomas with oligodendroglial differentiation and 5 pilocytic astrocytomas with oligodendroglial-like differentiation were negative for H09 immunohistochemistry. Three oligodendrogliomas with neurocytic differentiation had evidence of IDH1/IDH2 mutations either by H09 immunohistochemistry or direct sequencing. We conclude that in tumors with an oligodendroglioma-like morphology, binding of H09 is highly specific for oligodendrogliomas or oligoastrocytomas and substantially helps in the discrimination from other clear cell tumors. Negative H09 immunohistochemistry of an adult oligodendroglioma or oligoastrocytoma should prompt the consideration of other clear cell neoplasms. Further, our observations firmly assign oligodendrogliomas with neurocytic differentiation to the group of oligodendrogliomas and demonstrate that H09 is especially helpful for the difficult discrimination of such lesions from extraventricular neurocytomas.

The next generation of glioma biomarkers: MGMT methylation, BRAF fusions and IDH1 mutations

For some, glioma biomarkers have been expected to solve common diagnostic problems in routine neuropathology service caused by insufficient material, technical shortcomings or lack of experience. Further, biomarkers should predict patient outcome and direct optimal therapy for the individual patient. Unfortunately, current biomarkers still fall somewhat short of these grand expectations. While there has been some progress, it has generally been slow and in small steps. In this review, the newest set of glioma biomarkers: O(6) -methylguanine-DNA methyltransferase (MGMT) methylation, BRAF fusion and IDH1 mutation are discussed. MGMT methylation is well established as a prognostic/predictive marker for glioblastoma; however, technical questions regarding testing remain, it is not currently utilized widely in guiding patient management, and it has proven to be of no assistance in diagnostics. In contrast, BRAF fusion and IDH1 mutation analyses promise to be very helpful for classifying and grading gliomas, while their potential predictive value has yet to be established.