Neuroepithelial tumors of the central nervous system with fusion: a case report and literature review.

Neuroepithelial tumors (NEpT) harboring fusions remain an enigma. Initially described in sarcomas, these tumors display remarkable histomorphological diversity and unpredictable clinical behavior based on histologic or molecular features, with no established management protocols. To date, this subgroup of neoplasms has not been acknowledged as a entity by the WHO classification system, and it is currently designated as 'NEC'/'NOS'. This retrospective case series describes two young adults (32-35 years old) without cancer predisposition or risk factors, diagnosed with -fused NEpT. Case 1, a female with seizures, presented a heterogeneous left parietal lobe lesion (4.0 × 3.2 × 3.6 cm), classified as high-grade NEpT with promoter methylation, a calibrated score of 0.95 (≥ 0.9), and a co-occurring somatic mutation. Case 2, a male with chronic headaches and mild right-sided paresthesia, had a left frontotemporal lesion (3.0 × 2.8 × 3.4 cm), initially diagnosed as an extraventricular neurocytoma but later reclassified as a NEpT with low-to-intermediate grade features, without MGMT methylation, and a calibrated score of 0.92. Case 1 received upfront resection, followed by Stupp protocol chemoradiation and temozolomide maintenance, resulting in 14 months of progression-free survival (PFS). Case 2 underwent subtotal resection and adjuvant radiotherapy after an 8-month recurrence, achieving 11 months of PFS to date. Both patients are asymptomatic, off corticosteroids, with the latest imaging revealing no disease progression. Our cases emphasize that -fused NEpT displays a unique signature (ventricular localization, glioneuronal differentiation, and a distinct methylation cluster), supporting their inclusion in the WHO classification. Moreover, we present the first documented somatic co-mutation involving . At present, despite the theoretical risk of temozolomide resistance due to overexpression, our results suggest that conventional glioma therapies remain the preferred approach.