Droplet digital PCR is a powerful technique to demonstrate frequent FGFR1 duplication in dysembryoplastic neuroepithelial tumors.

Frédéric Fina,David T.W Jones,Dominique Figarella-Branger,L’Houcine Ouafik,Andrey Korshunov,Laëtitia Padovani,Didier Scavarda,Doriane Barets,Isabelle Nanni-Metellus,Corinne Bouvier,Carole Colin

doi:10.18632/oncotarget.12881

Abstract

Dysembryoplastic neuroepithelial tumors (DNT) share V600E mutation in the BRAF gene with other low grade neuroepithelial tumors (LGNTs). FGFR1 internal tandem duplication of the tyrosine-kinase domain (FGFR1-ITD), another genetic alteration that also leads to MAP kinase pathway alteration, has been previously reported in LGNTs by whole-genome sequencing. In the present study we searched for FGFR1-ITD by droplet digital PCR (DDPCR™) and for FGFR1 point mutations by HRM-sequencing in a series of formalin-fixed paraffin-embedded (FFPE) LGNTs including 12 DNT, 2 oligodendrogliomas lacking IDH mutation and 1p/19q co- deletion (pediatric-type oligodendrogliomas; PTOs), 3 pediatric diffuse astrocytomas (PDAs), 14 gangliogliomas (GGs) and 5 pilocytic astrocytomas (PAs). We showed by DDPCR™ that 5/12 DNT, but none of the other LGNTs, demonstrated FGFR1-ITD. In addition, these cases also accumulated phosphorylated-FGFR1 protein as shown by immunohistochemistry. FGFR1G539R point mutation was only recorded in one DNT that also showed FGFR1-ITD. Interestingly, these FGFR1 alterations were mutually exclusive from BRAFV600E mutation that was recorded in 13 LGNTs (3 DNTs, 1 PTO, 2 PDAs, 5 GGs and 2 PAs). Therefore, FGFR1 alteration mainly represented by FGFR1-ITD is a frequent event in DNT. DDPCR™ is an easy and alternative method than whole-genome sequencing to detect FGFR1-ITD in FFPE brain tumors, in routine practice.

Highlights

Dysembryoplastic neuroepithelial tumors (DNTs) are benign cortical tumors often occurring in the context of refractory epilepsy in children and young adults [1, 2] Two main histological forms of DNT have been described and are recognized by the 2016 WHO classification [3, 4]: 1/ the complex form and 2/ the simple form restricted to the glioneuronal element (GNE)
We report the detection of FGFR1 internal duplication by DDPCRTM in 5/12 DNT cases
We observed that FGFR1 duplication was never associated with BRAFV600E mutation, suggesting that in DNTs, as previously reported in pilocytic astrocytomas (PAs) and in other low grade neuroepithelial tumors (LGNTs) in children, these alterations are mutually exclusive [10, 11]

Summary

Introduction

Dysembryoplastic neuroepithelial tumors (DNTs) are benign cortical tumors often occurring in the context of refractory epilepsy in children and young adults [1, 2] Two main histological forms of DNT have been described and are recognized by the 2016 WHO classification [3, 4]: 1/ the complex form and 2/ the simple form restricted to the glioneuronal element (GNE). Some recurrent aberrations affecting FGFR1 have been reported in pediatric brain tumors including hotspot point mutations and a novel internal duplication of the kinase domain termed TKD-duplicated or FGFR1 internal tandem duplication (FGFR1-ITD). Another infrequent FGFR1 aberration that has been reported is the FGFR1-TACC1 fusion [9]. The FGFR1-ITD has first been reported in 1 case of PA by Jones and coworkers [10] and simultaneously in 13 LGNTs including 2 other PAs, 4 oligoastrocytomas, 3 diffuse astrocytomas, 3 oligodendrogliomas and 1 DNT by Zhang and coworkers [11] This second group has recently confirmed these results in a large study [12]. In these three recent reports [10,11,12], LGNTs were analyzed by whole-genome sequencing using frozen specimen, which is not suitable for routine diagnostic practice

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