Histopathological and molecular heterogeneity of dysembryoplastic neuroepithelial tumors.

Dysembryoplastic neuroepithelial tumors (DNTs) are low-grade glioneuronal tumors with FGFR1 alterations. They show significant histologic and molecular overlap with other glioneuronal tumors, complicating diagnosis. We analyzed 44 tumors that were either classified as DNT by DNA methylation (n = 37), or were diagnosed histologically as DNT but did not classify as DNT by DNA methylation (n = 7). 13/37 (35%) DNT-classifying tumors were histologically diagnosed as DNTs. High-confidence DNTs (score >0.9, 23 cases, 62%) demonstrated variable histology, most frequently DNT (39%), oligodendroglioma, and ganglioglioma and most frequently harbored FGFR1 alterations. Lower-confidence DNTs (score < 0.9, 14 cases, 38%) showed greater heterogeneity; their histologic diagnoses included papillary glioneuronal tumor, extraventricular neurocytoma, and pilocytic astrocytoma. Tumors with low confidence score exhibited diverse molecular alterations including BRAF V600E mutations, PDGFRA amplification, or multiple gene fusions. Among 7 histologically diagnosed DNTs that did not classify as DNT by methylation, most grouped with the myxoid glioneuronal PDGFRA-mutant class despite lacking canonical PDGFRA mutations. Thus, DNTs with high confidence scores are relatively homogenous but DNTs with low methylation confidence scores are heterogenous, highlighting the importance of integrated molecular profiling. Our findings also suggest that the myxoid glioneuronal tumor methylation class may require further classification of underlying drivers.