Decoding polymorphous low-grade neuroepithelial tumor of the young (PLNTY): Electroclinical features and molecular signatures in epilepsy surgery candidates.
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OBJECTIVES: Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) was recognized as a new histologic entity in the 2021 World Health Organization (WHO) classification of central nervous system tumors. It represents a distinct epileptogenic tumor, with about 80 cases reported to date across all age groups. The aim of this study is to describe the features of a cohort of PLNTY patients with a multimodal approach. METHODS: Patients diagnosed with PLNTY from 2014 to 2023 at our Institute were retrospectively reviewed to collect clinical, EEG, neuroimaging, histopathological, and molecular data. RESULTS: We identified 14 surgically treated patients (median age 21.5 years, range 12-46), with drug-resistant seizures in 78.6%. Seizure onset preceded surgery by a median period of 4 years (range .5-27). Bilateral interictal epileptiform EEG discharges and/or mislateralizing/mislocalizing ictal EEG discharge and/or semiological signs were found in 85.7% of patients, compared to 19.2% in a group of 26 non-PLNTY low-grade epilepsy-associated tumors (LEATs) (p < .001). All PLNTYs were supratentorial solid or solid-cystic cortical mass, involving the temporal (n = 8), temporo-occipital (n = 4), frontal (n = 1), or parietal lobe (n = 1). They featured an infiltrative growth pattern, oligodendroglioma-like cells, strong and often diffuse CD34 immunostaining, and frequent calcifications. Focal cortical dysplasia was associated in 14.3% of cases. Proliferation activity (MIB-1 labeling index) was very low (1%), except for one case (3%). BRAFV600E was found in 50% (n = 6/12) of cases, fibroblast growth factor receptor 3 (FGFR3) protein expression in 7 cases, 30.7% (n = 4/13) carried FGFR3 fusion. No fibroblast growth factor receptor 2 (FGFR2) fusion (n = 0/6) was identified. Postsurgical seizure outcome was excellent (Engel class I) in all cases. SIGNIFICANCE: This study confirms that, despite its name, PLNTY is not limited to pediatric patients. Findings underscore the highly epileptogenic nature of PLNTY and its recognizable electroclinical features, potentially related to its distinctive neuropathology. Most PLNTYs show mitogen-activated protein kinase (MAPK) pathway activating alterations, demonstrated by BRAFV600E mutation and FGFR3 fusion.