FGFR1::TACC1 fusion in mixed-morphology pediatric glioneuronal tumors: Report of two cases

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To the Editor, Pediatric low-grade gliomas and glioneuronal tumors often exhibit overlapping histological features that pose diagnostic challenges, particularly in small biopsy specimens. We present two pediatric cases of recurrent glioneuronal tumors with mixed histological patterns, both harboring FGFR1::TACC1 fusions detected by RNA-based next-generation sequencing (NGS). These cases emphasize the diagnostic complexity of such tumors and suggest a potential role for FGFR1::TACC1 as a molecular driver and therapeutic target. Case 1 is an 11-year-old boy who was admitted to the hospital with complaints of headache, morning nausea and balance disorder. He had undergone surgery for a right lateral intraventricular mass six years prior in his home country, with the pathological diagnosis being “Subependymal Giant Cell Astrocytoma.” Unfortunately, pathological material from the first operation could not be accessed, as it was performed in another country. On neurological examination, the cranial nerves were intact, with a positive Romberg sign. A contrast-enhanced brain MRI revealed a semisolid intraventricular mass located at the center of the right lateral ventricular body. The mass caused marked asymmetric dilation of the right lateral ventricle, pushing the septum pellucidum to the left by approximately 10 mm (Figure 1A and B). The mass contained cystic components in the anterosuperior section and a prominent solid component with diffuse heterogeneous contrast uptake in the posteroinferior section, measuring approximately 25 × 26 × 22 mm. The total dimensions of the mass were approximately 40 × 43 × 37 mm. Additionally, patchy hyperintense areas were observed in T2A and FLAIR sequences in the superior periventricular white matter, more prominent on the right, suggesting possible transependymal CSF passage. No intraaxial contrast uptake or diffusion limitation was detected (Figure 1A and B).

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