P20.02.b electro-clinical, neuroimaging features and neuropathological characterization of polymorphous low-grade neuroepithelial tumor of the young (plnty)

Abstract BACKGROUND Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) has been recently recognized by 2021 WHO Central nervous system classification. It is an epileptogenic tumor type, affecting mostly children and young adults, with peculiar radiological, and pathomolecular features. PLNTY is a very rare tumor, described in only 52 cases up to now. Herein, we describe 13 patients with electro-clinical and neuroimaging findings, associated to histopathological and molecular findings. MATERIAL AND METHODS We selected PLNTY patients from our Cancer Registry (Apr 2017-Dec 2022), and collected electro-clinical, radiological and histo-molecular data. Minimum follow-up was 6 months. Exams included EEG, long-term scalp video-EEG, pre-surgical brain computer tomography and Magnetic Brain Imaging (MRI). Immunohistochemistry included CD34, IDH1-R132H, GFAP, synaptophysin, ATRX, p53 and FGFR3. IDH1-2, BRAF (V600E) sequencing, Kiaa1549:BRAF, FGFR3:TACC3, FGFR2:kii1598 and FGFR2:CTNNA3 fusion analyses will be performed. RESULTS We describe 13 patients, median age 20.6 years (range 12.3-46.4). Most patients showed memory/executive impairment and had epilepsy, with an onset from 5 months-21 years before surgery. The main feature of seizures was a difficult localization and even lateralization, both semiologically and electrographically. Post-surgical seizure control was excellent.The tumors (n=11/13 temporal) presented as solid or solid-cystic cortical mass with no mass effect and unclear hedges. Calcifications were present in 4, and cysts in 6 cases. Microscopically the tumors showed infiltrative growth pattern, oligodendroglial-like cells, strong and often diffuse CD34 immunostaining, and frequent intra-tumoral calcifications. Malformation of cortical development, namely FCD type IIIB, was associated to PLNTY in 2 cases. Proliferation activity (MIB-1 LI) was very low (1%) in all cases except one (MIB-1 LI which reached 3%). CONCLUSION This study significantly extends the number of reported PLNTY associated to epilepsy, mostly characterized by bilateral interictal epileptiform discharges and difficult to lateralize seizures.The MRI features were heterogeneous and the differential diagnosis should include also dysplasia and glioneuronal tumors. PLNTY, despite its name, occurs also in adults, and electro-clinical and radiological diagnosis can be challenging. As recently described, PLNTY can show the MAPK pathway activating alterations, that are under investigation in our cohort to eventually clarify their role in the evolution of the disease. SUPPORT the study is partially supported by the Health Italian Minister (RC).