Pilocytic astrocytoma (PA) is a circumscribed low-grade glioma, typically defined by biphasic architecture, Rosenthal fibres, eosinophilic granular bodies, and MAPK pathway activation. However, PAs ma Show more
Pilocytic astrocytoma (PA) is a circumscribed low-grade glioma, typically defined by biphasic architecture, Rosenthal fibres, eosinophilic granular bodies, and MAPK pathway activation. However, PAs may sometimes display atypical morphologies, creating diagnostic dilemmas. DNA methylation profiling has emerged as a robust adjunct for resolving such ambiguity. We retrospectively analysed 68 gliomas with ambiguous histopathology. All underwent integrated work-up, including detailed histology, immunohistochemistry, fluorescence in situ hybridisation (FISH) for BRAF::KIAA Fusion, next-generation sequencing, transcriptomic profiling, and genome-wide DNA methylation profiling. Clinical and radiological data were reviewed with follow-up documentation. Out of 68 gliomas with ambiguous histopathological features, six cases were classified as pilocytic astrocytoma (PA) based on DNA methylation profiling. Ancillary molecular analyses revealed MAPK pathway alterations in all cases. The tumours occurred across cortical, midline, and infratentorial locations, exhibiting varied histomorphological appearances. Clinico-radiological correlation supported an indolent biological behavior, with all patients remaining alive and progression-free at 11-38 months of follow-up. Our findings emphasise the limitations of morphology-based diagnosis in histologically heterogeneous gliomas and demonstrate the critical role of DNA methylation profiling in establishing accurate classification. Adoption of integrated histological and molecular approaches is essential to avoid misclassification, prevent overtreatment, and improve prognostic assessment. Not applicable. Show less