MAPK pathway alterations in polymorphous low-grade neuroepithelial tumor of the young: diagnostic considerations

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently recognised tumor type with indolent behaviour with characteristic imaging and histomolecular features. We describe the clinical, imaging, histo-molecular features of 15 cases diagnosed as low-grade glioma suggestive of PLNTY, over a period of 3 years. Immunohistochemistry (IHC) and fluorescence in situ hybridisation were used to assess molecular alterations. The tumors were seen predominantly in children (range 5-65 years). Most of the patients presented with history of seizures. Imaging revealed cortical-subcortical well demarcated solid-cystic tumor with intratumoral calcification. Histopathology revealed a low-grade tumor with oligodendroglia-Iike cells admixed with astrocytic cells immunopositive for CD34. BRAF p.V600E mutations and FGFR2 breakapart were observed in six cases each, while three showed FGFR3 breakapart. FGFR2 breakapart positive PLNTY were seen in children exclusively. The majority of cases were seizure free post-surgery, except two patients who succumbed to the illness. PLNTY, needs to be considered as a prime differential diagnosis in a solid-cystic tumor in a young patient with history of seizures. Characteristic clinical features, radiology, histomorphology with an IHC panel of OLIG2, GFAP and CD34 correlates with one of the MAPK alterations in PLNTY (BRAF p.V600E, FGFR2/3 gene rearrangement). In a resource limited setting, this limited panel may be sufficient for a correlative diagnosis.