Our data provide the necessary reevaluation of the impact of surgery in molecularly defined LGG and support maximal resection as first-line treatment for molecularly defined LGG. Importantly, in IDH mutated astrocytoma, even small postoperative volumes have negative impact on OS, which argues for a second-look operation in this subtype to remove minor residues if safely possible.
Targeted NGS allows a clinically relevant classification of diffuse glioma into groups with very different outcomes. The diagnosis of diffuse glioma should be primarily based on a molecular classification, with the histopathological grade added to it. Future discussion should primarily aim at establishing the minimum requirements for molecular classification of diffuse glioma.
Background
The Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT-NOW) has recommended that isocitrate dehydrogenase 1 and 2 wildtype (IDH1/2wt) diffuse lower-grade gliomas (LGGs) World Health Organization (WHO) grade II or III that present with (i) a telomerase reverse transcriptase promoter mutation (pTERTmt), and/or (ii) gain of chromosome 7 combined with loss of chromosome 10, and/or (iii) epidermal growth factor receptor (EGFR) amplification should be reclassified as diffuse astrocytic glioma, IDH1/2 wildtype, with molecular features of glioblastoma, WHO grade IV (IDH1/2wt astrocytomas WHO IV). This paper describes the overall survival (OS) of IDH1/2wt astrocytoma WHO IV patients, and more in detail patients with tumors with pTERTmt only.
Methods
In this retrospective multicenter study, we compared the OS of 71 IDH1/2wt astrocytomas WHO IV patients, with radiological characteristics of LGGs, with the OS of 197 IDH1/2wt glioblastoma patients. Moreover, we compared the OS of 22 pTERTmt only astrocytoma patients with the OS of the IDH1/2wt glioblastoma patients.
Results
Median OS was similar for IDH1/2wt astrocytoma WHO IV patients (23.8 mo) and IDH1/2wt glioblastoma patients (19.2 mo) (Cox proportional hazards model: hazard ratio [HR] 1.27, 95% CI: 0.85–1.88, P = 0.242). OS was also similar in patients with IDH1/2wt astrocytomas WHO IV, pTERTmt only, and IDH1/2wt glioblastomas (HR 1.15, 95% CI: 0.64–2.10, P = 0.641).
Conclusions
The presented data confirm the cIMPACT-NOW recommendation and we propose that IDH1/2wt astrocytomas WHO IV in the absence of other qualifying mutations should be classified as IDH1/2wt glioblastomas.
Cancer cells are genomically unstable and accumulate tumor type-specific molecular aberrations, which may represent hallmarks for predicting prognosis and targets for therapy. Co-deletion of chromosomes 1p and 19q marks gliomas with an oligodendroglioma component and predicts a better prognosis and response to chemotherapy. In the current study, we present a novel method to detect chromosome 1p/19q co-deletion or loss of heterozygosity (LOH) in a diagnostic setting, based on single-nucleotide polymorphism (SNP) analysis and next-generation sequencing (NGS). We selected highly polymorphic SNPs distributed evenly over both chromosome arms. To experimentally determine the sensitivity and specificity of targeted SNP analysis, we used DNAs extracted from 49 routine formalin-fixed, paraffin-embedded glioma tissues and compared the outcome with diagnostic microsatellite-based LOH analysis and calculated estimates. We show that targeted SNP analysis by NGS allows reliable detection of 1p and/or 19q deletion in a background of 70% of normal cells according to calculated outcomes, is more sensitive than microsatellite-based LOH analysis, and requires much less DNA. This specific and sensitive SNP assay is broadly applicable for simultaneous allelic imbalance analysis of multiple genomic regions and can be incorporated easily into NGS mutation analyses. The combined mutation and chromosomal imbalance analysis in a single NGS assay is suited perfectly for routine glioma diagnostics and other diagnostic molecular pathology applications.
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