[Supratentorial papillary glioneuronal tumors: a clinicopathological and genetic analysis of six cases].
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Objective: To investigate the clinicopathological and genetic characteristics of papillary glioneuronal tumor (PGNT) and to reclassify cases according to the integrated pathologic-molecular diagnosis with the 2021 World Health Organization (WHO) classification of tumors of central nervous system (CNS). Methods: Six tumors diagnosed as PGNT at the Sanbo Brain Hospital, Capital Medical University from January 2010 to August 2025 were collected. Their clinical, imaging, histopathological, and molecular data were retrospectively analyzed. Comprehensive profiling was conducted using hematoxylin and eosin staining, immunohistochemistry, targeted next-generation sequencing, RNA sequencing, and DNA methylation analyses. Results: All tumors were located in the supratentorial cerebral hemispheres. Among the 6 patients, there were 4 males and 2 females, aged 17.0 (10.0, 25.5) years old. Histology revealed a characteristic papillary structure. In four cases, focal and sheet-like neurocytic cells were observed in interpapillary regions, meanwhile two cases showed scattered suspicious ganglion or neuronal cells. Mitoses were rare. The case 4 exhibited focal anaplasia features within the tumor. The papillary-forming cells showed diffuse immunoreactivity for GFAP, OLIG2, S-100, and SOX10. Cells in the interpapillary areas exhibited diffuse or partial synaptophysin positivity, with focal and diffuse positivity for NeuN and calretinin in four cases. The Ki-67 proliferation index was mostly<5% (only one case showed a focal increase to 8%). All cases were negative for IDH1-R132H, H3K27M, and BRAF V600E. Cases 3 to 6 harbored SLC44A1::PRKCA fusions. Cases 1 and 2 had KIAA1549::BRAF and STRIP2::BRAF fusions, respectively. Based on the integrated pathologic-molecular diagnosis, the cases 3 to 6 were definitively classified as PGNT, CNS WHO grade 1, while the case 4 showed focal anaplasia. By integrated with DNA methylation profiling, the case 1 and 2 were reclassified as low-grade glioma/low-grade glioneuronal tumor, not elsewhere classified. The 6 patients underwent craniotomy with gross total or subtotal tumor resection. One of them also received local radiotherapy. At the last follow-up (July 2025), all patients were alive without recurrence or progression. The overall survivals were 105, 50, 66, 64, 12, and 6 months, respectively. Conclusions: PGNT is a rare glioneuronal tumor characterized by a biphasic pattern with pseudopapillary glial architectures and interpapillary neuronal components. The presence of focal and sheet-like NeuN-positive neurocytic cells in the interpapillary regions is a significant diagnostic clue for PGNT. Integrated pathologic-molecular analysis is essential for accurately classifying supratentorial papillary glioneuronal tumors. Classic PGNTs are molecularly defined by recurrent PRKCA fusions, while BRAF-altered cases warrant reclassification.