The genomic landscape of dysembryoplastic neuroepithelial tumours and a comprehensive analysis of recurrent cases

AIMS: Dysembryoplastic neuroepithelial tumour (DNT) is a glioneuronal tumour that is challenging to diagnose, with a wide spectrum of histological features. Three histopathological patterns have been described: specific DNTs (both the simple form and the complex form) comprising the specific glioneuronal element, and also the non‐specific/diffuse form which lacks it, and has unclear phenotype–genotype correlations with numerous differential diagnoses. METHODS: We used targeted methods (immunohistochemistry, fluorescence in situ hybridisation and targeted sequencing) and large‐scale genomic methodologies including DNA methylation profiling to perform an integrative analysis to better characterise a large retrospective cohort of 82 DNTs, enriched for tumours that showed progression on imaging. RESULTS: We confirmed that specific DNTs are characterised by a single driver event with a high frequency of FGFR1 variants. However, a subset of DNA methylation‐confirmed DNTs harbour alternative genomic alterations to FGFR1 duplication/mutation. We also demonstrated that a subset of DNTs sharing the same FGFR1 alterations can show in situ progression. In contrast to the specific forms, “non‐specific/diffuse DNTs” corresponded to a heterogeneous molecular group encompassing diverse, newly‐described, molecularly distinct entities. CONCLUSIONS: Specific DNT is a homogeneous group of tumours sharing characteristics of paediatric low‐grade gliomas: a quiet genome with a recurrent genomic alteration in the RAS‐MAPK signalling pathway, a distinct DNA methylation profile and a good prognosis but showing progression in some cases. The “non‐specific/diffuse DNTs” subgroup encompasses various recently described histomolecular entities, such as PLNTY and diffuse astrocytoma, MYB or MYBL1 altered.