MOLECULAR MARKERS OF GLIOMAS Implications for diagnosis and new target therapies

The 2016 WHO classification of gliomas integrates molecular alterations (ie IDH mutations, and 1p19q codeletion) to histological features, defining distinct histo-molecular entities: IDH wild-type gliomas (mostly glioblastomas), and IDH mutated gliomas, divided according to 1p19q status into astrocytomas (1p19q intact) and oligodendrogliomas (1p19q codeleted). The first part of the manuscript is a contribution to molecular classification based on TERT promoter mutational status. We also contributed to GWAS analysis, and investigated the association between the risk loci and specific molecular entities, showing that some loci are associated with glioblastoma and IDH wild-type gliomas (rs2736100 near RTEL1, rs6010620 near TERT, rs3851634 near POLR3B) whereas others are associated to IDH mutated gliomas (rs4295627 and rs55705857 near CCDC26, rs498872 near PHLDB1, rs7572263 near IDH1, rs11196067 near VTI1A, rs648044, near ZBTB16 and rs12230172). Notably, rs4295627 and rs55705857 near CCD26 resulted strongly associated to 1p19q codeletion and to risk of oligodendrogliomas (P=2.31 x10-94). The second part of this work is devoted to the characterization of a specific oncogenic fusion between FGFR and TACC genes, which initially reported 3% of glioblastoma (GBM) and other human cancers and is proposed as a new therapeutic target. Overall, we screened 907 gliomas for FGFR3-TACC3 fusions. We found that FGFR3-TACC3 fusions exclusively affect IDH wild-type gliomas (3%), and are mutually exclusive with the EGFR amplification and the EGFR vIII variant, whereas it co-occurs with CDK4 amplification, MDM2 amplification and 10q loss. FGFR3–TACC3 fusions were associated with strong and homogeneous FGFR3 immunostaining. We show that FGFR3 immunostaining is a sensitive predictor of the presence of FGFR3-TACC3 fusions. FGFR3-TACC3 glioma patients had a longer overall survival than those patients with IDH wild-type glioma. We treated two patients with FGFR3–TACC3 rearrangements with a specific FGFR-TK inhibitor and we observed a clinical improvement in both and a minor response in one patient. These data support the systematic screening for FGFR-TACC fusion in all IDH wild-type glioma patients who can benefit from FGFR inhibition. In the third section, we developed a non-invasive diagnostic tool by 1H-magnetic resonance spectroscopy in IDH mutant gliomas. We optimized a uniquely different spectroscopy sequence called MEGA-PRESS for the detection of the oncometabolite 2-hydroxyglutarate (2 HG) that specifically accumulates in IDH mutant gliomas. We analysed a prospective cohort of 25 patients before surgery for suspected grade II and grade III gliomas and we assessed specificity and sensitivity, correlation with 2 HG concentrations in the tumor and associations with grade and genomic background. We found that MEGA-PRESS is highly specific (100%) and sensitive (80%) for the prediction of IDH mutation and correlated with 2 HG levels measured by gas chromatography-tandem mass spectrometry (GC-MS/MS) in frozen tissue. Preliminary follow-up during radio-chemotherapy regimen and anti-IDH therapy showed a decrease in 2 HG production. In conclusion, MEGA-PRESS is a reliable tool for IDH mutation prediction at pre-surgical stages and for measuring the activity of anti-cancer drugs. Long-term monitoring will help to clarify the prognostic and predictive value of 2 HG decrease during anti-cancer treatment.