Nanopore and EPIC array profiling unmask an atypical non-midline H3 K27-altered glioma: a case report.

We report a rare case of Diffuse Midline Glioma, H3K27-altered, arising in a non-midline fronto-temporo-insular location in a 48-year-old adult, initially mimicking Glioblastoma, IDH-wildtype, based on radiology and histopathology. Integrated molecular diagnostics, including genome-wide DNA methylation profiling and Sanger sequencing, confirmed an H3.3 K27M mutation, while Nanopore-based methylation profiling provided a rapid and fully concordant classification, demonstrating the feasibility of real-time epigenomic diagnostics in clinical practice. H3K27M-mutant diffuse non-midline gliomas (DNMG) are extremely rare, with only ~39 cases reported in the literature, most commonly involving the temporal lobe and associated with poor prognosis. Our case highlights that DNMGs can present in adults and in previously unreported hemispheric locations, underscoring the importance of integrated molecular testing not only for accurate diagnosis but also to guide patient management and enable enrollment in potential targeted therapies. Molecular profiling thus represents a critical tool for personalized treatment planning and prognostic assessment in these uncommon gliomas.